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In 3G, the most prevalent technology was UMTS with CDMA-2000 in close contention. All radio access technologies have to solve the same problems: to divide the finite RF spectrum among multiple users as efficiently as possible. GSM uses TDMA and FDMA for user and cell separation. UMTS, IS-95 and CDMA-2000 use CDMA. WiMAX and LTE use OFDM.
These phones include combination of GSM and CDMA technology. They can be used as a GSM or CDMA phone according to the user's preference. These handsets are also called global phones. An example of this is the Samsung SCH-A790. These dual-mode handsets are compatible with both GSM and CDMA networks and are essentially two phones in one device.
Mobile virtual network operators (MVNOs) in the United States lease wireless telephone and data service from the four major cellular carriers in the country—AT&T Mobility, Boost Mobile, T-Mobile US, and Verizon—and offer various levels of free and/or paid talk, text and data services to their customers.
The top five wireless providers operate nationwide wireless networks which cover most of the population in the United States, while smaller carriers provide native network coverage across selected regions of the United States while supplementing nationwide coverage through roaming agreements with other carriers.
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G [1] mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible successor to second-generation cdmaOne (IS-95) set of standards and used especially in North America ...
The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system for networks based on the GSM standard. [1] Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the International Telecommunication Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing cdmaOne technology.
IMT-2000 CDMA Direct Spread. also known as W-CDMA, used in UMTS, the successor to GSM; IMT-2000 CDMA Multi-Carrier. also known as CDMA2000, the successor to 2G CDMA ; IMT-2000 CDMA TDD. also known as TD-SCDMA; IMT-2000 TDMA Single Carrier. also known as EDGE, an intermediate 2.5G technology; IMT-2000 FDMA/TDMA. also known as DECT
Although both are different and independent from one another, both the CDMA and UMTS networks use the 850 and 1900 MHz frequencies. Bell's LTE network uses Band 4 Advanced Wireless Services (AWS 1700/2100 MHz) and Band 2 Personal Communications Service (PCS 1900 MHz) in most coverage areas and Band 7 (2600 MHz) in a few areas.