So I'm on a family plan with my parents and sister with AT&T, but after my first semester at College in Maine, I realized that AT&T doesn't have any service up there so I'm trying to switch to T-Mobile. I also have a regular cell phone because smart phones are pretty expensive on AT&T, but with T-Mobile no contract a month it would be the same price to have a smart phone. So I want to switch to one of my sister's old IPhone 3. I'm in good standing with AT&T, but their unlocked page is down also I know my phone is eligible to keep it's same number when I switch. Any help would be great, thanks.

My contracts already over and I don't want there to be a time when I don't have any service.