Can I sell a T-mobile phone if I owe money on the last account it was activated on?

I have a blackberry that I want to sell but it was activated on my boyfriends plan and he terminated the contract but never paid the termination fee. Can I sell it or will t-mobile not let the phone be activated on someones else's account?Can I sell a T-mobile phone if I owe money on the last account it was activated on?Since T-Mobile uses GSM network and uses sim cards on there cell phones it doesn't matter what cell phone you use as long as it is compatible with T-Mobile and has a sim card holder inside the phone. So there would not be a problem selling your Blackberry to another T-Mobile user since all they need to do is to insert a T-Mobile sim card into the cell phone. T-Mobile would not know it is tied to another person's account.