It should be, it should work with any carrier CDMA or GSM. Just buy the Sim card for which towers you want to use. GSM Sim is Att and CDMA is Verizon.
Per the Specs: Universal Unlocked
Compatible with all major U.S. carriers, including Verizon, AT&T, Sprint and T-Mobile. Also compatible with prepaid carriers including Cricket Wireless, Boost Mobile, MetroPCS, Simple Mobile, Total Wireless, Tracfone, Net10, Mint, and H2O.