Sure you can. Apple already has a very impressive distribution channel in place. They sell more ipods in their own stores than all other retailers put together.

Apple is the king of distribution. It would have been very simple to put them on shelves and include a link or form for people to signup with the provider since the phone is unsubsidized anyway.

Now they have limited their audience to those willing to go to ATT, which rules out everyone that hates ATT or those in contract with another provider.