Sorry but Molly and Rafe totally missed the ball on this one. In Australia, Canada and the UK and many other countries, the iPhone is already sold by Apple out of contract online and at Apple stores, without any carrier involvement, just pop in any sim you have into the phone and it works on all carriers in these countries. It's still sold at carriers locked if you want it subdised, but the only reason this can not work in the US is the incomparable standards and spectrums carriers use, making it impossible to easily build a phone that works on all networks, so Apple stuck with the exclusivity deal.
The problem is that the lack of a sim card actually makes it a lot harder to sell the iPhone without a carrier, as the carrier would have to support this new simless feature. This is only a move by Apple to make the iPhone thinner by removing the space the sim slot takes internally, at the cost of more difficulty for the consumer in picking a carrier.