This list of GSM providers may not be complete. Please check with your provider before purchasing a phone.
Major carriers:
AT&T
T-Mobile
U.S. Carriers
AirFire Mobile
Alaska Communications (no-annual contract plans only, prepaid phones are CDMA)
ASTAC
Big Sky Mobile
Cellular One of East Central Illinois
Cellular One Nation
Choice Wireless (retail location in Wichita Falls, TX, formerly known as Cellular One TXOK; not to be confused with the Choice Wireless subsidiary of Commnet Wireless)
Cordova Wireless
Cricket Wireless
DTC Wireless
Epic PCS
GCI Wireless (maintains a GSM and CDMA network; contact provider for more information)