While the whole web seems to be speculating that the incoming iPhone 5 will pack "global" LTE support, including the venerable Wall Street Journal, there's a significant chance that we'll be fat out of luck in the UK, and here's why.
We're used to our 3G phones being global phones, or to put it in other words, it'll work just fine in any country that has a GSM network. That's because 3G networks are broadcast across the world using only a few select bands of radio spectrum. That means one radio in your phone can cover all these bands, and hop between them when you travel about the globe (as long as you don't mind being raped for data charges that is).
LTE, on the other hand, can use a wide range of bands, and in fact, most countries in the world seem to be using different bands of the electromagnetic spectrum than everywhere else. Of course, there is overlap, such as the 1800MHz band Everything Everywhere is pushing being used in a few European countries, but apparently there are some 41 LTE bands potentially in use about the world for 4G networks.
This is a serious issue for radio chipmakers, who have their work cut out for them in trying to cover all the bands with just one radio. Qualcomm has a "programmable" radio, but that means tuning it to specific bands in specific countries and that can't be done on the fly. Essentially, there's a lot of work be done before we can be in a position to have a 4G "world phone" and we're certainly not there yet.
So, what does that really mean for us here in the UK? Well, for the iPhone 5, there's a distinct possibility that Apple won't bother (or can't because of the timing) roll out an iPhone 5 with an LTE chip that supports Everything Everywhere's 4G 1800MHz LTE band. Of course, with Europe slightly ahead of the game compared to the UK, there's also the possibility that the iPhone 5 will support EE's 4G network, once it's up and running. But, when the other networks roll out their respective networks using the 800MHz and 2600MHz bands, it's unlikely that the iPhone 5 will support both those bands, so you'll be limited to EE, if you get 4G at all, or, possibly, just the ones using 800MHz, once the spectrum auction completes.
Does that matter? Well, it might mean being locked-in to Everything Everywhere for your 4G service. Of course, it'll still work on 3G on every network, so it's not like it'll be a complete dud. Just don't get your hopes up for a UK 4G-capable iPhone come Wednesday this week; it's just as likely to be 3G-only (or severely limited) for us Brits, and that would be a shame. [WSJ, Ubergizmo, Wikipedia]