Already have an iphone, bought 6 weeks ago when the price dropped in the UK to 169, and unlocked to work with my work-provided SIM.
Will I change to the new version? Yes, as long as I can unlock it. By the sounds of it, I'll need to sign a contract in store to get a new iphone, and I'm not really interested in that though unless they do a cheap data only rate.
Major reason for changing? Tomtom. At the moment I use a Windows Mobile device for Tomtom navigation: if the iphone can do that as well as everything it does, it's the one device I need...
