if you're buying the iphone 6 or 6 plus at full retail price unlocked with any carrier, it's best to buy the variants with the cellular and wireless chipsets a1524 and a1586. these 2 variants cover all the cellular frequencies and technologies used on the planet.....including the unique td-scdma rf modulation used in china mobile's 3g. also, there's td-lte support for 4 bands in china.
CDMA EV-DO Rev. A and Rev. B (800, 1700/2100, 1900, 2100 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
TD-SCDMA 1900 (F), 2000 (A)
GSM/EDGE (850, 900, 1800, 1900 MHz)
FDD-LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
TD-LTE (Bands 38, 39, 40, 41)