I think at the moment, your carrier is the only way to purchase the phone off-contract so you can remain under your plan. I have to go through Verizon to keep my unlimited plan so I imagine it's the same as AT&T.
I kept mine with no problems last year.
I don't see why not.
Apple and other retailers can do the upgrade without changing anything on your account. Best buy should be the same.
You can also call them and ask.
ATT allows you to continue your unlimited plan, as long as its on your account you should be able to upgrade anywhere and keep unlimited data. Ive never had a problem, just make sure you let them know to keep your unlimited data
I think at the moment, your carrier is the only way to purchase the phone off-contract so you can remain under your plan. I have to go through Verizon to keep my unlimited plan so I imagine it's the same as AT&T.
Its not the same thing with AT&T and verizon.
Different carriers, different rules.
With AT&T you don't have to pay full price. You can get a full subsidy and still keep your unlimited data.