Change to other carrier

Hey guys, im sure you can help.

A friend of mine has registered his blackberry with t-mobile and used it there before but now he changed to o2 (other German carrier) and wants to use this blackberry with their sin card, what's there to do now? O2 says that t-mobile has to deactivate the imei on their system first before he can use his bis on o2.

Does anyone know if it's possible to do this on your own?

Thanks guys!!

He has to call T-Mobile Customer service or tech support and get them to delete his BIS account with them