The original cellular technology was based on an analog signal. During the 1990s the new PCS digital mobile phone technology was introduced. PCS stood for Personal Communication System, and Sprint being one of the first companies to adopt this started their digital phone division, called Sprint PCS.
AMPS
This technology is mentioned for historical purposes. Although radio phones or a proto cell phone technology can be traced back to the 1950s, Advanced Mobile Phone System (AMPS) is considered the first true cell phone network commercially available to the United States, starting in 1978.
AMPS communication was unencrypted, so people to listen in on cell phone conversations with an ordinary police scanner. Phones were often cloned, causing issues of fraud and network abuse. AMPS was also a bandwidth hog, using a Frequency-division multiple access (FDMA) scheme that required significant amounts of wireless spectrum.
AMPS started to get phased out beginning in the 1990s when PCS digital was introduced.
Verizon Wireless operated an AMPS network, and on February 18, 2008, Verizon discontinued all AMPS service. The last of the AT&T AMPS network was shut down February 18, 2008.
GSM
GSM stands for Global System for Mobile Communications; it's the world's most prolific mobile standard. This is what you will find if you are, say for example, traveling in Europe.
Most new phones on AT&T and T-Mobile actually adhere to both GSM and the newer UMTS (Universal Mobile Telecommunications System) standards. UMTS isn't an official part of the GSM standard, but it is what GSM carriers use for 3G data transmission.
Phones using GSM can do both voice and data at the same time, which cannot be done with CDMA.
Switching Providers: GSM phones use a removable Sim Card. If the phone is unlocked you can pop a SIM card out of a GSM phone and stick it in any other GSM phone, switching a phone from one provider to another.
CDMA
CDMA stands for Code Division Multiple Access, including both CDMAOne or CDMA 2000. This is the most common standard in the United States of America throughout the 1990's and until present (2012).
CDMA2000, based more directly on its predecessor includes a range of improvements over the original CDMAOne, key among them 3G data speeds.
CDMA phones have a slightly more refined method for handing off calls from tower to tower, so they drop fewer calls as compared to GSM.
Switching Providers: CDMA phones ship locked to one network, and can only be switched to another with the cooperation of both the old and new carriers.
TDMA
This is an outdated technology. The major TDMA carriers switched over to GSM. AT&T (including the former AT&T Wireless) and US Cellular were formerly on the TDMA standard. US Cellular actually went to CDMA.
U.S. Providers and Technologies
- Verizon - CDMA, UMTS
- AT&T Mobility - GSM, UMTS, HSDPA
- Sprint - CDMA, UMTS
- Nextel - iDEN
- US Cellular - CDMA
- T-Mobile - GSM, UMTS, GAN
- Cricket Communications - CDMA
- Virgin Mobile - CSMA
A Mobile Virtual Network Operator (MVNO) is a cell phone company that doesn't own any wireless spectrum, but instead buys it from a network operator such as Sprint. Essentially, an MVNO is a marketing company that believes it can build a profitable business targeting niche markets such as Hispanics or teenagers. Prior to 2006, most MVNOs offered prepaid service, with TracFone and Virgin Mobile among the notable-name providers.
Roaming
A CDMA-only phone from Verizon, Sprint, or US Cellular is only able to roam on other CDMA networks. This is fine in North America, but CDMA networks are rare in Europe and other countries. These three carriers offer phones with built-in GSM support for International traveling, but this feature is missing from their most popular handsets.
Using Another Provider's Phone With Verizon, Sprint, or US Cellular
Verizon's phones and network are CDMA, which doesn't use sim cards.
CDMA phones do not use sim cards, while GSM phones do.
CDMA and GSM are different technologies that are incompatible with each other.
The term "unlocking" referring to an unlocked phone is used when discussing GSM and iDEN phones.
There are other CDMA providers besides Verizon, which include Sprint and US Cellular.
Verizon will only activate another Verizon phone. A non-Verizon CDMA phone's ESN number will not be in Verizon's database of phones, and therefore, Verizon will not activate it.
Mobile Broadband Data
Mobile broadband is also known as 3G, or third-generation cell-phone technology. Both GSM and CDMA have developed their own 3G technology solutions for delivering high-speed Internet access to mobile devices.
The CDMA-based mobile broadband technology is called EV-DO.
The GSM mobile broadband technology is called HSDPA.
1xEVDO