You can use the phone and some of the internet features, but things like VVM will not work, and the internet may have issues as the BB feature would be on the rate plan. Having said that it should work fine (although you may get IMs from AT$T warning of the wrong data plan on the device, assuming you have a data plan as not all AT$T BB require them, at least that was the case over 2 years ago when I had one, may be required now).