H2O Micro / Mini SIM Card for any Unlocked GSM Phone w/ $40 Airtime H2O 2-in-1 SIM Card (Standard and Micro) - $40 Airtime 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.