Microsoft Lumia 535 RM-1092 Dual SIM Factory Unlocked Cell Phone, US Version, 8GB, Black Microsoft Lumia 535 features 1.2 GHz quad-core 3G Network 850/900/1900/2100 8GB Internal Memory 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.