Is it possible that AT&T might offer phones without a fixed-duration contract, but locked to their network?
So even if they do offer options such as pay-as-you-go; users still won't have the option of cancelling and switching to another provider.
No, but they might have the option of selling via E-bay to Europe (at more than the price of purchase) and there somebody might unlock it.
(Anyway I thought locking is illegal, or least unlocking is legal in the US. Locking is certainly illegal in Europe, but that will only apply to stuff officially sold in Europe.)
iPhone.