Which iPhone 5 models are compatible with cellular carriers around the globe? 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.

GSM model A1428: UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 4 and 17)
CDMA model A1429: CDMA EV-DO Rev. A and Rev. B (800, 1900, 2100 MHz); UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 1, 3, 5, 13, 25)
GSM model A1429: UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 1, 3, 5)

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.