I am visiting New York in June and plan on bringing a 3G iPad back with me.
They are not locked to a carrier so we can swap for a uk sim card back here, I'm sure I read vodafone supports microsims now, either way somebody will shortly as the ipad is due to land here by months end!
My only concern is the software, you sign up for data via iPad, is it going to know we have inserted a different sim and adjust options and plans accordingly? I'm hoping it will be just like vodafone when I switched iPhone carrier, sync to iTunes with new sim and it will download a .ipcc carrier file then the settings will auto install over the air. To be honest we won't know until someone tries, by the time I go, we should know.
Hope this helps.