Microsoft Lumia 535 Dual SIM Unlocked GSM Cell Phone Network GSM 850 / 900 / 1800 / 1900 3g Network Hsdpa 900 / 2100 (Green) Microsoft Lumia 535 Black features 1.2 GHz quad-core Dual Sim Unlocked Cell Phone 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.