One of the best things about the iPhone 4S was that it rolled GSM and CDMA into the same baseband. What that means is if you have, say, an AT&T iPhone, it could technically run on Verizon as long as you unlocked it. Likewise, if you had a Verizon iPhone, you could just slap in a GSM pay-as-you-go SIM card if you were traveling in any other country in the world to avoid exorbitant international roaming fees.
With the iPhone 5, though, things are changing. There will be two versions of the iPhone 5, a separate device for both GSM and CDMA carriers. Why? Seems to all be about LTE.
According to Apple’s official specs page, there will be three versions of the iPhone 5. First, there’s A1428 GSM version and an A1429 CDMA version. They both support LTE, HSPA+ and DC-HSPA, but they do so on different bands, with the 1428 working on AT&T and various Canadian operators carrying LTE support on bands 4 and 17, while the A1429 will work with Verizon and Sprint and offer LTE on bands 1, 3, 5, 13 and 25. The last iPhone 5 is the GSM A1429 variant, and will be offered mostly in global markets.
What this means is that, once again, if you buy an AT&T iPhone 5 or a Verizon iPhone 5, you’re pretty much locked to that carrier. Bummer.