AT&T is always GSM, T-Mobile is always GSM, while Verizon and Sprint are always CDMA. You can also generally assume that if it uses a SIM card to get online, it's a GSM iPhone, though some iPhone models like the iPhone 4S have both CDMA and GSM capabilities.
Just so, is iPhone 7 a GSM phone?
By comparison, all iPhone 6s and iPhone 6s Plus models worked on both GSM and CDMA networks. A customer that purchases an iPhone 7 from Apple's website and selects Verizon as their carrier, on the other hand, would also be able to use the smartphone on AT&T, T-Mobile, Sprint, or any other GSM or CDMA network.
Is the iPhone 5c unlocked?
Verizon: All 4G devices, including the iPhone 5, 5s, and 5c are unlocked as a matter of corporate policy; AT&T: This phone is locked when you purchase it from its stores. It can be unlocked by calling technical support at 800-331-0500 or by going to its web site.
Is iPhone 5s GSM compatible?
The only big difference is that the Verizon version also includes CDMA support. And the AT&T and T-Mobile GSM versions do not. Sprint's version of the iPhone 5S doesn't support all the same frequencies as the iPhone 5S made for AT&T and T-Mobile or the one made for Verizon.