I have this problem too. I thought this would be solved when I connected the device to my computer and was asked by itunes if I would like to 'register' this iphone and did so but the problem persists. In other words, the phone keeps asking me to enter my password when i try to 'view account'. However, that same page also offers a button where I can 'sign out'.
I have a iphone 4 running IOS 4.1. Its an unlocked At&t phone.