Wireless Tmobile Help

hi guys, i just found this site and hope to be able to contribute as much as possible. hopefully someone can help me out. i just picked up a clients laptop in which he has a tmoble/sony erricson wireless card where you insert your sim card to get access. He move the sim card from the phone to the card. is that they way that works. i am not familiar with sims cards. the card works if using wifi. however when you isnert the sim card and access that way, the whole computer shuts off. im thinking its a conflict problem. does anyone know what to do here. any help will be appriciated. thanks