As of 2015, AT&T and T-Mobile are among the most popular cellular carriers utilizing GSM technology in the United States. Compared to the competing technology, CDMA, GSM features better international coverage and better support for unlocking cellphones for the purpose of moving to another carrier.
Outside of the United States, most networks use GSM technology. As GSM comes from an industry consortium, and CDMA is owned by chipmaker Qualcomm, manufacturers face a smaller overhead when building equipment using GSM.
Popular cellular carriers that use CDMA include Verizon, Sprint and U.S. Cellular. Users praised CDMA technology, touting its better overall call quality compared to GSM, upon its introduction into the industry.