While the best unlocked phones almost certainly support GSM carriers like AT&T and T-Mobile, it’s best to look for devices that work with all the major U.S. providers, including Verizon.

In the U.S., AT&T and T-Mobile are GSM carriers. Contrast with CDMA phone. See GSM. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction requires permission.

The company offered service under the Cellular One brand in most regions. Although originally a TDMA carrier in most areas, the company migrated to GSM technology.

A multi-carrier GSM phone with two, three or four SIM cards. Dual-SIM phones are popular with global travelers who use local and foreign carriers as well as people who want a business and personal ...