Companies such as Nokia and Motorola already have deals with the major networks to promote and subsidise their phones and won't take too kindly to any newcomers muscling in on their patch.
The networks will undoubtedly want to do a deal with apple, but apple are not known for their co-operation with others, and the networks won't want to upset the likes of Nokia with their proven popularity.
I wouldn't be surprised if you had to pay the full price of �200+ for the phone if you really want one, and then probably not on all networks.