[CrackBerry Question]

i tried the at&t go card sim but blackberry rejected it. also i couldnt find the imei number anywhere not even in the about-hardware search.. do i even need an imei to operate any sim card or is that only for at&t sim cards? and i didnt like the at&t sim card cuz it was small, and i had to put it in the plastic to make it fit the tray for the playbook, and it was such a hassle and still didnt work. please advise. thanks