Originally Posted by pedro_cesar
I have to call the previous BB phone owner or the previous Data Service Owner?
Yep. That is the best way to do it. Sometimes a carrier will do it for you, but you have to prove it is your device.
Just as an FYI, here is an article from our FAQ on buying used BBs: Buying a BlackBerry off eBay - BlackBerryFAQ
Shows some of the problems you might run into.