Garage Sale Cell Phone makes calls

I just bought a Cingular cell phone at a garage sale to resell on Ebay. I was cleaning it up and it rang. I did not answer it, but tried to make a call on it and it worked. It is a Sony Ericcson T62U with a SIM card. Are these prepaid or what? Or is it still on someones account? Any help would be appreciated.

i guess whoever sold it to you didnt cancel it or its a stolen phone. if you really want to sell it just take the sim card out. if the person that sold it to you didnt get the service canceled, thats their bad. you could take it back to the person and ask if they forgot to cancel the service.