On this page Apple lists 3 different models of iPhone with different LTE support. My question is, if I buy an iPhone in one area (e.g. Canada), and take it back to another area (e.g. the UK), what network compatibility can I expect on my device? (both LTE coverage as well as just working for voice and data at any speeds)
The tech specs page lists the available network features per model in more detail.
In short, the two biggest differences are the CDMA vs. the GSM models. Depending on what you get, you won't even be able to do voice calls on the other type of network.
Across the two different models with GSM antennas, it appears that the same frequencies for everything but LTE are supported, so you are likely to get 3G and GPRS support across all GSM networks if the carrier supports it.
It's pretty clear that the two GSM models will not work on any CDMA carrier whether or not you jailbreak it or get an authorized unlock.
It also is very clear that the CDMA model will work on pretty much any GSM carrier in the 3G/4G range of speeds (but not LTE). I have a Verizon CDMA A1429 model that works perfectly fine with my AT&T account (I've not cancelled that service yet and went in for a SIM card - took 10 minutes to switch from VZW to AT&T including the time the rep was in the back getting my SIM card.)
So - if you want the most flexibility, hands down the A1429 model is the most broadly compatible on the 3G as well as 4G band count. The only reason to get a different model would be price considerations (subsidy / contract termination fee / choice of provider) or you really wanted LTE in bands 4 or 17.
Apple's technical specifications page makes it very easy to tell which device to get from a cellular data and frequency standpoint since everything is spelled out.
Ok, I’m gonna explain it very simple, non-technical terms.
This is what Apple lists on their tech specs page:
The A1429 wins hands down. It can work on most networks in the world, though you won’t get LTE speeds on all of them. The highest you can be assured of is 3G speeds. You can also make voice calls send texts on most, if not all, with the A1429.