there was an initial mix-up between my old iphone 4 and my girlfriend's new iphone 4s. thanks to the good folks at at&t, when she set up her 4s it somehow was got assigned my phone number. after going to the store and getting new sim cards i thought this problem was solved. now when she tries to buy something from itunes or app store on her phone it asks for my apple id. how can i fix this, please?
Go to "settings >> store", tap on your I'd and select "sign out" from the options provided. Next time you try to purchase something you will be prompted to enter a new login and password and you should be able to enter a different one.