I'm still waitin for my ipad2, but I've got my unlimited plan and SIM card on the side. Who has successfully swapped over their old SIM? Did you have to call ATT? Did you just swap it over with no call to ATT?
If you remember your original iPad AT&T login info, go here:
http://www.att.com/ipadlanding
If you can log in successfully, you can change your IMEI and ICCID numbers from the old iPad to the new one. No need to change SIM cards and you retain your grandfathered unlimited plan, if you had it originally.
Remember that unfortunately the bad people scam the carriers, which impacts us.
I highly suggest you call AT&T.
Your new device has a unique identifier. If you do _not_call they assume you're a scammer and will usually revoke your plan. You've been advised.
I called ATT on friday and they asked me for the new IMEI, told me to swap SIMs and reboot...