I'd love to see more freedom of choice here. Tying phones to contracts just seems so needlessly anti-consumer.
Are phones more expensive in Europe in general and are less often subsidized? Also, what's a SIM-only plan?
A SIM-only plan is a plan where you don't buy a phone at all from the carrier, just a SIM card. You then plug it into a phone you already have (or buy separately, unsubsidized.)
US carriers don't generally encourage their customers to buy phones direct from the manufacturers, but the GSM carriers (T-Mobile and AT&T) both have no problems with it (as well they wouldn't, given they don't have to subsidize the phone then.) IS-95 carriers like Sprint PCS and Verizon tend to be a little weirder on the whole "You mean a customer bought his own phone?" thing.
Either way, US operators don't reward customers for purchasing unsubsidized equipment. For people like me, who do it anyway, the advantages are the phones haven't been crippled by the carrier, and roaming in an area not covered by a roaming agreement is just a matter of using a prepaid SIM from a carrier that actually covers the area. (I'm a T-Mobile customer, but some areas around have Cingular coverage only, and for some reason T-Mobile users can only use some Cingular towers, not all of them. So I carry a PAYG GoPhone card for situations where I need that.)
On a separate note, I really disbelieve all the nonsense that Apple is trying to foist a consumer-friendly contractless regime on the carriers, and this initial lock-in is just a way to get a foot in the door. Apple's exclusivity with AT&T is for five years. That's a long time to be standing at the door.
Truth be told, I think Apple just wants the expense of the phone to be part of its appeal. It's something special, something that costs a little bit more, but is "worth it". They know they'll never gain a majority market share, but they can ensure the iPhone is perceived to be more valuable, and that the money will come in for many years, as the iPod's sales slowly decline against an onslaught of slowly more credible MP3 playing phones.