Here is couple of interesting articles I found:

1. You can enter 99 9999 99 as your social security number during activation in iTunes. Once AT&T can’t verify your credit and then it will offer pre-paid options, so you won’t get locked into a two year contract.

2. You can activate with a hacked iTunes and a activation server. You can’t use the phone portion, but wifi and rest works. See:

3. Also has some interesting threads…

SIM unlock should be available hopefully