These are the bands that model A1634 supports.
1. A1634: The iPhone 6S Plus A1634 is the GSM & CDMA phone and it has the same cellular connectivity as the A1633. The phone is available on AT&T as well as some more GSM carriers in the US like Boost, NET10, Cricket, US Cellular or StraightTalk. You can also pay full price for the iPhone 6S Plus as Apple is selling it as the sim-free unlocked version. Specifically, it supports LTE bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29, 30; TD-LTE bands 38, 39, 40, 41; GSM/EDGE (850, 900, 1800, 1900 MHz); TD-SCDMA 1900 (F), 2000 (A); CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz) and UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz).