There is much speculation here as to who the carrier will be for UK/European Market. Orange and T-Mobile have been ruled out for a variety of reasons namely software branding issues with Orange and appalling service from T Mobile.
If 3 managed to get their teeth into the iPhone it would also be a coup of huge proportions but 3 is probably the worst UK/European carrier ever that I think Apple would be off their minds to jump in with them. BT/O2 are in the mood to build strategic partners as is Vodafone.
Many of the UK carriers are offering huge discounts and lock in deals at the moment; the market is truly mature and the iPhone may be just the stimulus needed to get things moving again.
O2 and Vodafone are my bets at the moment.
There also an increasing appetite for Apple products in Europe following the ipod. I'm seriously looking at updating to a Mac. Windows and MS Office have just about gone as far as they need to go. Vista is pretty but power sapping.
The iPhone could be the wedge Apple needs to open the crack in Windows community that will allow the Mac et al to flood in and fill the void.