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Cell Phone
A mobile telephone or cellular telephone (commonly "mobile phone" or "cell
phone") is a long-range, portable electronic device used for mobile
communication. In addition to the standard voice function of a telephone,
current mobile phones can support many additional services such as SMS for text
messaging, email, packet switching for access to the Internet, and MMS for
sending and receiving photos and video. Most current mobile phones connect to a
cellular network of base stations (cell sites), which is in turn interconnected
to the public switched telephone network (PSTN) (the exception is satellite
phones).
History
History of mobile phones
Various cell phones from the past 10–15 years.
Legend:
1. NEC Cellstar 500 series (Early 1990s)
2. Nokia 2110 series (1994)
3. Nokia 5120 (1998)
4. Kyocera 2135 (2002)
5. Audiovox CDM8300 (2002)
6. Samsung SCH-A650 (2004)
There is one U.S. Patent Number 887357 for a wireless telephone, issued 1908 to
Nathan B. Stubblefield of Murray, Kentucky. He applied this to "cave radio"
phones and not directly to cellular telephony as we know it today. However, the
introduction of cells for mobile phone base stations, invented in 1947 by Bell
Labs engineers at AT&T, was further developed by Bell Labs during the 1960s.
Radiophones have a long and varied history going back to Reginald Fessenden's
invention and shore-to-ship demonstration of radio telephony, through the Second
World War with military use of radio telephony links and civil services in the
1950s, while hand-held cellular radio devices have been available since 1983.
Due to their low establishment costs and rapid deployment, mobile phone networks
have since spread rapidly throughout the world, outstripping the growth of fixed
telephony.
In 1945, the zero generation (0G) of mobile telephones was introduced. 0G mobile
telephones, such as Mobile Telephone Service, were not officially categorized as
mobile phones, since they did not support the automatic change of channel
frequency during calls, which allows the user to move from one cell (the base
station coverage area) to another cell, a feature called "handover".
In 1970, Bell Labs invented such a "call handoff" feature, which allowed
mobile-phone users to travel through several cells during the same conversation.
Motorola is widely considered to be the inventor of the first practical mobile
phone for handheld use in a non-vehicle setting. Using a modern, if somewhat
heavy portable handset, Motorola manager Martin Cooper made the first call on a
handheld mobile phone on April 3, 1973.
The first commercial cellular network was launched in Japan by NTT in 1979.
Fully automatic cellular networks were first introduced in the early to mid
1980s (the 1G generation) with the Nordic Mobile Telephone (NMT) system in 1981.
This was followed by a boom in mobile telephone usage, particularly in Northern
Europe.
The first "modern" network technology on digital 2G (second generation) cellular
technology was launched by Radiolinja (now part of Elisa Group) in 1991 in
Finland on the GSM standard which also marked the introduction of competition in
mobile telecoms when Radiolinja challenged incumbent Telecom Finland (now part
of TeliaSonera) who ran a 1G NMT network. A decade later, the first commercial
launch of 3G (Third Generation) was again in Japan by NTT DoCoMo on the WCDMA
standard. Until the early 1990s, most mobile phones were too large to be carried
in a jacket pocket, so they were typically installed in vehicles as car phones.
With the miniaturization of digital components, mobile phones have become
increasingly handy over the years.
Manufacturers
The mobile phone manufacturers can be grouped into two. The top five are
available in practically all countries and comprise about 75% of all phones
sold. A second tier of small manufacturers exists with phones mostly sold only
in specific regions or for niche markets. The top five in order of market share
are Nokia, Motorola, Samsung, SonyEricsson and LG.
Nokia Corporation is currently the world's largest manufacturer of mobile
telephones, with a global device market share of approximately 36% in Q1 of
2007. Other mobile phone manufacturers include Apple Inc., Audiovox (now UT
Starcom), Benefon, BenQ-Siemens, High Tech Computer Corporation (HTC), Fujitsu,
Kyocera, LG Mobile, Mitsubishi, Motorola, NEC, Neonode, Panasonic (Matsushita
Electric), Pantech Curitel, Philips, Research In Motion, Sagem, Samsung, Sanyo,
Sharp, Siemens, Sierra Wireless, SK Teletech, Sonim Technologies, Sony Ericsson,
T&A Alcatel,Toshiba, and Verizon. There are also specialist communication
systems related to (but distinct from) mobile phones, such as Professional
Mobile Radio.
Subscriptions
This Railfone found on some Amtrak trains uses cellular technology.See also:
List of mobile network operators
Several countries, including the UK, now have more mobile phones than people.
There are over five hundred million active mobile phone accounts in China, as of
2007. Luxembourg has the highest mobile phone penetration rate in the world, at
164% in December 2001. In Hong Kong the penetration rate reached 117% of the
population in September 2004. The total number of mobile phone subscribers in
the world was estimated at 2.14 billion in 2005. The subscriber count reached
2.7 billion by end of 2006 according to Informa. Around 80% of the world's
population enjoys mobile phone coverage as of 2006. This figure is expected to
increase to 90% by the year 2010.
At present, Africa has the largest growth rate of cellular subscribers in the
world, its markets expanding nearly twice as fast as Asian markets. The
availability of prepaid or 'pay as you go' services, where the subscriber is not
committed to a long term contract, has helped fuel this growth to a monumental
scale in Africa as well as in other continents.
On a numerical basis, India is the largest growth market, adding about 6 million
cell phones every month. With 156.31 million cell phones, market penetration in
the country is still low at 17.45% India expects to reach 500 million
subscribers by end of 2010.
There are three major technical standards for the current generation of mobile
phones and networks, and two major standards for the next generation 3G phones
and networks. All European countries and African countries and many Asian
countries have adopted a single system, GSM, which is the only technology
available on all continents and in most countries and covers over 74% of all
subscribers on mobile networks. In many countries, such as the United States,
Australia, Brazil, India, Japan, and South Korea GSM co-exists with other
internationally adopted standards such as CDMA and TDMA, as well as national
standards such as iDEN in the USA and PDC in Japan. Over the past five years
several dozen mobile operators (carriers) have abandoned networks on TDMA and
CDMA technologies switching over to GSM. None have switched away from GSM.
With third generation (3G) networks which are also known as IMT-2000 networks,
about three out of four networks are on WCDMA (also known as UMTS) standard,
usually seen as the natural evolution path for GSM and TDMA networks. One in
four 3G networks is on the CDMA2000 1x EV-DO technology. Some analysts count a
previous stage in CDMA evolution, CDMA2000 1x RTT, as a 3G technology whereas
most standardization experts count only CDMA2000 1x EV-DO as a true 3G
technology. Because of this difference in interpreting what is 3G, there is a
wide variety in subscriber counts. As of June 2007, on the narrow definition
there are 200 million subscribers on 3G networks. By using the more broad
definition, the total subscriber count of 3G phone users is 475 million.
While some systems of payment are 'pay as you go' where conversation time is
purchased and added to a phone unit via an Internet account or in shops or ATMs,
other systems are more traditional ones where bills are paid by regular
intervals. Pay as you go (also known as "pre-pay") accounts were invented
simultaneously in Portugal and Italy and today form more than half of all mobile
phone subscriptions. USA, Canada, Japan and Finland are among the rare countries
left where most phones are still contract-based.
Culture and customs
In less than twenty years, mobile phones have gone from being rare and expensive
pieces of equipment used primarily by the business elite to a pervasive low-cost
personal item. In many countries, mobile phones now outnumber land-line
telephones, with most adults and many children using mobile phones. In the
United States, 50% of children are using mobile phones. In many young adults'
households the mobile phone has supplanted land-line telephones. In some areas
in developing countries with scarce fixed-line infrastructure, the mobile phone
has introduced telephony as such. It has given poor people in isolated
communities access to services such as medical and legal advice. However, the
mobile phone is also banned in some countries like North Korea.
With high levels of mobile telephone penetration, mobile culture has evolved
where the phone is a key social tool with people relying on their mobile phone
address book to keep in touch with friends, not least by SMS, and a whole
culture of "texting" has developed from this. Since the first person-to-person
SMS text message was sent in Finland in December 1993, today "texting" has
become the most widely used data service on the planet, with 1.8 billion people
as active users of SMS texting and the service generated 80 billion dollars of
service revenues in 2006 (source ITU). Many phones offer Instant Messenger
services to increase the simplicity and ease of texting on phones. Mobile phones
in Japan, offering Internet capabilities such as NTT DoCoMo's i-mode, offer text
messaging via standard e-mail. In several countries internet access from mobile
phones has become used by more internet users than access from PCs. Japan was
first, followed by South Korea, China and India. In Europe several countries
have proportions of 30%–40% of all internet users now accessing via mobile
phones. Most mobile internet access is significantly different from PC based
internet access, with services such as alerts, weather information, e-mail,
search, IM and downloads of games and music favored over classic "web browsing".
Most mobile internet use is of short duration and in a hurry.
The mobile phone itself has also become a fashion object of totemic value, with
users decorating, customizing, and accessorizing their mobile phones to reflect
their personality. This has emerged as its own industry. The sale of commercial
ringtones exceeded 5 billion in 2006 according to Informa.
Etiquette
The use of a mobile phone is prohibited in some train company carriagesMobile
phone etiquette has become an important issue with phones ringing at funerals,
weddings,toilets,cinemas, and plays. Users often speak at increased volume which
has led to places like book shops, libraries, bathrooms, movie theaters,
doctors' offices, and houses of worship posting signs prohibiting the use of
mobile phones, and in some places installing signal-jamming equipment to prevent
usage (although in many countries including the United States, such equipment is
currently illegal). Some new buildings such as auditoriums have installed wire
mesh in the walls (turning the building into a Faraday cage) which prevents any
signal getting through, but does not contravene the jamming laws.
Trains, particularly those involving long-distance services, often offer a
"quiet car" where phone use is prohibited, much like the designated non-smoking
car in the past. However many users tend to ignore this as it is rarely
enforced, especially if the other cars are crowded and they have no choice but
to go in the "quiet car". Mobile phone use on aircraft is also prohibited and
many airlines claim in their in-plane announcements that this prohibition is due
to possible interference with aircraft radio communications even though this has
been proven to be completely untrue. There is no interference from mobile phones
that remain turned to aircraft avionics, as the airline safety staff well know
as a typical airliner has dozens of phones that were forgotten to be turned off,
on every flight. The real nuisance of phones that are on while planes take off
and land, is that they disrupt the mobile phone networks on the ground. With
busy airports landing jumbo jets every few minutes, the ground based mobile
phone networks would experience continuous peaks in brief traffic overloads as
hundreds of passenger phones would attempt to connect to the ground base
stations.
As customers want to be connected on planes, now several airlines are
experimenting with tiny base stations and antenna systems installed into the
cabin of the airplane, allowing low power short range connection of any phones
onboard to maintain a connection to the base station in the plane. In this way
they would not attempt to find connection to the ground base stations as the
planes take off and land. At the same time the airlines could offer phone
services to their travelling passengers either as full voice and data servies,
or initially only as SMS text messaging and similar services. Qantas the
Australian airline is the first airline to run a test airplane in this
configuration in the Autumn of 2007. Emirates have announced plans to allow
limited mobile phone usage on some flights.
In any case, there are inconsistencies between practices allowed by different
airlines and even on the same airline in different countries. For example,
Northwest Airlines may allow the use of mobile phones immediately after landing
on a domestic flight within the US, whereas they may state "not until the doors
are open" on an international flight arriving in the Netherlands. In April 2007
the US Federal Communications Commission officially grounded the idea of
allowing passengers to use phones during a flight.
In a similar vein signs are put up in UK petrol stations prohibiting the use of
mobile phones due to possible safety issues. Most schools in the United States
have prohibited mobile phones in the classroom due to the large number of class
disruptions that result from their use, the potential for cheating via text
messaging, and the possibility of photographing someone without consent. In the
UK, possession of a mobile phone in an examination can result in immediate
disqualification from that subject or from all their subjects.
Use in disaster response
The Finnish government decided in 2005 that the fastest way to warn citizens of
disasters was the mobile phone network. In Japan, mobile phone companies provide
immediate notification of earthquakes and other natural disasters to their
customers free of charge. In the event of an emergency, disaster response crews
can locate trapped or injured people using the signals from their mobile phones
or the small detonator of flare in the battery of every cellphone; an
interactive menu accessible through the phone's Internet browser notifies the
company if the user is safe or in distress. In Finland rescue services suggest
hikers carry mobile phones in case of emergency even when deep in the forests
beyond cellular coverage, as the radio signal of a cellphone attempting to
connect to a base station can be detected by overflying rescue aircraft with
special detection gear. Also, users in the United States can sign up through
their provider for free text messages when an Amber Alert goes out for a missing
person in their area.
Use by drivers
One phone in each hand Mobile phones and driving safety
Mobile-phone use while driving is common but controversial. While few
jurisdictions have banned motorists from using mobile phones while driving
outright, some have banned or restricted drivers from using hand-held mobile
phones while exempting phones operated in a hands-free fashion. It is generally
agreed that using a hand-held mobile phone while driving is a distraction that
brings risk of road traffic accidents. However, some studies have found
similarly elevated accident rates among drivers using hands-free phones,
suggesting that the distraction of a telephone conversation itself is the main
safety problem.
Use of handheld mobile phones by drivers is illegal in many European countries
and a number of Asian and South American countries and Australia. Use of
hands-free mobiles is permitted, although the Australian states of New South
Wales and Victoria have banned hands free for learner and first year
provisional/probationary licence holders. In Greece the use of mobile phone and
hands free has been banned, while the use of bluetooth technology is permitted.
However some countries like Japan ban mobile phone use while driving completely.
Similar laws exist in six U.S. states with legislation proposed in 40 other
states. The United States Department of Defense has outlawed the use of all
mobile phones while driving on any DOD installation, unless a hands-free device
is used. In Israel, it is common practice to pull over to the side of the road
where possible to answer a mobile phone. In Croatia law prohibits usage of
mobile phones while crossing the road as a pedestrian.
Applications
Mobile news services are expanding with many organizations providing "on-demand"
news services by SMS. Some also provide "instant" news pushed out by SMS. Mobile
telephony also facilitates activism and public journalism being explored by
Reuters and Yahoo and small independent news companies such as Jasmine News in
Sri Lanka. Also companies like Monster are starting to offer mobile services
such as job search and career advice.
The total value of mobile data services exceeds the value of paid services on
the internet, and was worth 31 billion dollars in 2006 (source Informa). The
largest categories of mobile services are music, picture downloads, videogaming,
adult entertainment, gambling, video/TV.
Power
Mobile phones generally obtain power from batteries which can be recharged from
mains power, a USB port or a cigarette lighter socket in a car. Formerly, the
most common form of cell phone batteries were nickel metal-hydride, as they have
a low size and weight. Lithium-Ion batteries are sometimes used, as they are
lighter and do not have the voltage depression that nickel metal-hydride
batteries do. Many mobile phone manufacturers have now switched to using
lithium-Polymer batteries as opposed to the older Lithium-Ion, the main
advantages of this being even lower weight and the possibility to make the
battery a shape other than strict cuboid. Cell phone manufacturers have been
experimenting with alternate power sources.
This short section requires expansion.
Features
Mobile phone features
There are significant questions as to who first invented the camera phone, as
numerous other people received patents filed in the early 1990s for the device,
including David M. Britz of AT&T Research in March of 1994 and Phillipe Kahn,
who claims to have first invented it in 1997. The camera phone now holds 85% of
the mobile phone market. Mobile phones often have features beyond sending text
messages and making voice calls, including Internet browsing, music (MP3)
playback, memo recording, personal organizer functions, e-mail, instant
messaging, built-in cameras and camcorders, ringtones, games, radio,
Push-to-Talk (PTT), infrared and Bluetooth connectivity, call registers, ability
to watch streaming video or download video for later viewing, video calling and
serve as a wireless modem for a PC, and soon will also serve as a console of
sorts to online games and other high quality games (e.g. Final Fantasy Agito).
When cellular telecoms services were launched, phones and calls were very
expensive and early mobile operators (carriers) decided to charge for all air
time consumed by the mobile phone user. This resulted in the concept of charging
callers for outbound calls and also for receiving calls. As mobile phone call
charges diminished and phone adoption rates skyrocketed, more modern operators
decided not to charge for incoming calls. Thus some markets have "Receiving
Party Pays" models, in which both outbound and received calls are charged, and
other markets have "Calling Party Pays" models, by which only making calls
produces costs, and receiving calls is free. An exception to this is
international roaming, by which also receiving calls is normally also charged.
The European market adopted a "Calling Party Pays" model throughout the GSM
environment and soon various other GSM markets also started to emulate this
model. As Receiving Party Pays systems have the undesired effect of phone owners
keeping their phones turned off to avoid receiving unwanted calls, the total
voice usage rates (and profits) in Calling Party Pays countries outperform those
in Receiving Party Pays countries. Consequently, most countries previously with
Receiving Party Pays models have either abandoned them or employed alternative
marketing methods, such as massive voice call buckets, to avoid the problem of
phone users keeping phones turned off.
In most countries today, including European nations, Kazakhstan, Romania,
Turkey, New Zealand, Korea, Japan, Pakistan, Australia, Bulgaria, Brazil, Chile,
Colombia, India, Maldives, Peru, South Africa, Israel, Lebanon and Jordan the
person receiving a mobile phone call pays nothing. However, in Hong Kong,
Canada, and the United States, one can be charged per minute. In the United
States, a few carriers are beginning to offer unlimited received phone calls.
For the Chinese mainland, it was reported that both of its two operators will
adopt the caller-pays approach as early as January 2007.
Forensics and evidence
Law enforcement globally rely heavily upon mobile telephone evidence, to the
extent that in the EU the "communications of every mobile telephone user are
recorded" . The concerns over terrorism and terrorist use of technology prompted
an inquiry by the British House of Commons Home Affairs Select Committee into
the use of evidence from mobile telephone devices, prompting leading mobile
telephone forensic specialists to identify forensic techniques available in this
area. NIST have published guidelines and procedures for the preservation,
acquisition, examination, analysis, and reporting of digital information present
on cell phones can be found under the NIST Publication SP800-101.
An example of criminal investigations using mobile phones is the initial
location and ultimate identification of the terrorists of the 2004 Madrid train
bombings. In the attacks, mobile phones had been used to detonate the bombs.
However, one of the bombs failed to detonate, and the SIM card in the
corresponding mobile phone gave the first serious lead about the terrorists to
investigators. By tracking the whereabouts of the SIM card and correlating other
mobile phones that had been registered in those areas, police were able to
locate the terrorists.
Human health impacts
Mobile phone radiation and health
Since the introduction of mobile phones, concerns have been raised about the
potential health impacts from regular use. As mobile phone penetrations grew
past fixed landline penetration levels in 1998 in Finland and from 1999 in
Sweden, Denmark and Norway, the Scandinavian health authorities have run
continuous long term studies of effects of mobile phone radiation effects to
humans, and in particular children. Numerous studies have reported and most
studies consistently report no significant relationship between mobile phone use
and health. Studies from the Institute of Cancer Research, National Cancer
Institute and researchers at the Danish Institute of Cancer Epidemiology in
Copenhagen for example showed any link between mobile phone use and cancer. The
Danish study only covered analog mobile phone usage up through 1995, and
subjects who started mobile phone usage after 1995 were counted as non-users in
the study. The health concerns have grown as mobile phone penetration rates
throughout Europe reached 80%–90% levels earlier in this decade and prolonged
exposure studies have been carried out in almost all European countries again
most reporting no effect, and the most alarming studies only reporting a
possible effect. However, a study by the International Agency for Research on
Cancer of 4,500 users found a statistically significant link between tumor
frequency and mobile phone use.
Environmental impacts
The typical hysteria around mobile phones and mobile networks is seen in the
widely reported and immediately totally discredited claim that mobile phone
masts are associated with the "Colony Collapse Disorder" (CCD) which has reduced
bee hive numbers by up to 75% in many areas, especially near cities in the US.
The Independent newspaper cited a scientific study claiming it provided evidence
for the theory that mobile phone masts are a major cause in the collapse of bee
populations, with controlled experiments demonstrating a rapid and catastrophic
effect on individual hives near masts. Mobile phones were in fact not covered in
the study, and the original researchers have since emphatically disavowed any
connection between their research, mobile phones, and CCD, specifically
indicating that the Independent article had misinterpreted their results and
created "a horror story". It should be pointed out that if this CCD would be
caused by mobile phones, then beekeepers in countries with advanced use of
mobile phones such as those in Scandinavia, Italy, Portugal, Austria etc should
have seen these effects years earlier than the USA. But this finding was
uniformly and globally dismissed by all from the telecoms industry to animal
safety experts and even beekeepers worldwide. While the initial claim of damage
to bees was widely reported, the corrections to the story were almost
non-existent in the media.
Technology
See also: Cellular frequencies
Mobile phone tower
Cell Phone tower located in Lynnwood, WA.Mobile phones and the network they
operate under vary significantly from provider to provider, and country to
country. However, all of them communicate through electromagnetic radio waves
with a cell site base station, the antennas of which are usually mounted on a
tower, pole or building.
The phones have a low-power transceiver that transmits voice and data to the
nearest cell sites, usually not more than 5 to 8 miles (approximately 8 to 13
kilometers) away. When the mobile phone or data device is turned on, it
registers with the mobile telephone exchange, or switch, with its unique
identifiers, and will then be alerted by the mobile switch when there is an
incoming telephone call. The handset constantly listens for the strongest signal
being received from the surrounding base stations. As the user moves around the
network, the mobile device will "handoff" to various cell sites during calls, or
while waiting (idle) between calls it will reselect cell sites.
Cell sites have relatively low-power (often only one or two watts) radio
transmitters which broadcast their presence and relay communications between the
mobile handsets and the switch. The switch in turn connects the call to another
subscriber of the same wireless service provider or to the public telephone
network, which includes the networks of other wireless carriers. Many of these
sites are camouflaged to blend with existing environments, particularly in
scenic areas.
The dialogue between the handset and the cell site is a stream of digital data
that includes digitized audio (except for the first generation analog networks).
The technology that achieves this depends on the system which the mobile phone
operator has adopted. The technologies are grouped by generation. The first
generation systems started in 1979 with Japan, are all analog and include AMPS
and NMT. Second generation systems started in 1991 in Finland are all digital
and include GSM, CDMA and TDMA. Third generation networks are still being
deployed, started with Japan in 2001, are all digital and offer high speed data
access in addition to voice services and include WCDMA known also as UMTS, and
CDMA2000 EV-DO. China will launch a third 3G technlogy on the TD-SCDMA standard.
Each network operator has a unique radio frequency band.
Books about mobile communication
Since 2002, many books have been written on the social impact of mobile phones:
Agar, Jon, Constant Touch: A Global History of the Mobile Phone, 2004 ISBN
1840465417
Ahonen, Tomi, m-Profits: Making Money with 3G Services, 2002, ISBN 0-470-84775-1
Ahonen, Kasper and Melkko, 3G Marketing 2004, ISBN 0-470-85100-7
Glotz, Peter & Bertsch, Stefan, eds. Thumb Culture: The Meaning of Mobile Phones
for Society, 2005
Katz, James E. & Aakhus, Mark, eds. Perpetual Contact: Mobile Communication,
Private Talk, Public Performance, 2002
Kavoori, Anandam & Arceneaux, Noah, eds. The Cell Phone Reader: Essays in Social
Transformation, 2006
Levinson, Paul, Cellphone: The Story of the World's Most Mobile Medium, and How
It Has Transformed Everything!, 2004 ISBN 1-4039-6041-0
Ling, Rich, The Mobile Connection: the Cell Phone's Impact on Society, 2004 ISBN
1558609369
Ling, Rich and Pedersen, Per, eds. Mobile Communications: Re-negotiation of the
Social Sphere, 2005 ISBN 1852339314
Nyíri, Kristóf, ed. Mobile Communication: Essays on Cognition and Community,
2003
Nyíri, Kristóf, ed. Mobile Learning: Essays on Philosophy, Psychology and
Education, 2003
Nyíri, Kristóf, ed. Mobile Democracy: Essays on Society, Self and Politics, 2003
Nyíri, Kristóf, ed. A Sense of Place: The Global and the Local in Mobile
Communication, 2005
Nyíri, Kristóf, ed. Mobile Understanding: The Epistemology of Ubiquitous
Communication, 2006
Plant, Dr. Sadie, on the mobile – the effects of mobile telephones on social and
individual life, 2001
Rheingold, Howard, Smart Mobs: The Next Social Revolution, 2002 ISBN 0738208612
Terminology
Related non-mobile-phone systems
Cordless telephone (portable phone)
Cordless phones are standard telephones with radio handsets. Unlike mobile
phones, cordless phones use private base stations that are not shared between
subscribers. The base station is connected to a land-line. Increasingly, with
wireless local loop technologies, namely DECT, the distinction is blurred.
Professional Mobile Radio
Advanced professional mobile radio systems can be very similar to mobile phone
systems. Notably, the IDEN standard has been used as both a private trunked
radio system as well as the technology for several large public providers.
Similar attempts have even been made to use TETRA, the European digital PMR
standard, to implement public mobile networks.
Radio phone
This is a term which covers radios which could connect into the telephone
network. These phones may not be mobile; for example, they may require a mains
power supply. Also, they may require the assistance of a human operator to set
up a PSTN phone call.
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