Samsung Galaxy Ace S5831 - Factory Unlocked GSM 3G 900/2100 Smartphone White Factory Unlocked to GSM Networks Multi-Touch Screen Wi-Fi Stereo FM Radio Unlocked cell phones are compatible with GSM carriers like AT&T and T-Mobile as well as with GSM SIM cards (e.g. H20, Straight Talk, and select prepaid carriers). Unlocked cell phones will not work with CDMA Carriers like Sprint, Verizon, Boost or Virgin.