okay so, my older sister, for my birthday is adding a line to her cell phone plan so i can have a cell. she is letting me pick out the phone that i want. but can u pick anyphone to put on the plan? she has only 2 phones on her plan so far and i think its unlimited text and 700 minues to share everymonth. so if i go in to the att store and pick out say, an iphone, would that be added onto the plan with no problem..exept having to pay for the phone itself. or does it have to be one they choose