I'm planning to buy (in the US) an iPad model 64GB with WiFi and 3G. I live part time in the US and part time in Mexico, and I would like to have 3G data service in both countries. I know the primary 3G provider for the iPad in the US is AT&T and the primary 3G provider in Mexico is TelCel. I have read that the "stock" iPad 3G is "unlocked", but I'm unclear if this means only that the AT&T 3G service is optional, or if stock the iPad 3G can use any 3G service, like TelCel in Mexico. Do I need to do further unlocking to use the iPad 3G in both countries?