Nokia Lumia 620 Black Factory Unlocked Smartphone Cellular Band - Quad-Band 850 / 900 / 1800 / 1900 Mhz Cellular Band 3G - 850 / 900 / 1900 / 2100 Mhz 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.