Comment Re:VOIP instead of roaming (Score 2, Informative) 158
O2 is one of the better UK providers in that respect. My iPhone was locked originally, but I went with O2 because at the time (mid-2010) they said they would unlock it properly at the end of the contract period. No jailbreaks, no risk of bricking after software updates, etc.
Now it turns out that they will unlock it even before the end of the contract (though I'm still on the hook for the monthly fee till the end, of course). Just have to ask them.
O2 are great for their signal, but their pricing does take the piss.
When you've finished your contract; maybe try Giffgaff. There's no phone support (it all online), so they're a lot cheaper (£10/mo for unlimited data and text, and 250 mins) - and they still use the O2 network. The support you get from the community is astounding, and they do pay people back quite a lot for helping out.
They've even got a wiki to help you unlock your phone. Definitely worth a look.