We have an account with Verizon. At the moment we have a MiFi and where we live I may as well try to stand on the roof and catch Internet. So I am considering getting an iPad (1st gen) with 3G. Can I just buy one and it will work for Verizon? Half the ones on amazon don't list the cellphone carrier so I want to be sure when I buy one that it can be used interchangably between AT&T and Verizon.