Porting cell phone number to Verizon?

I currently have AT&T wireless service (formerly Cingular), but I am not in a contract. My 2 year contract expired in April, and now it has gone month-to-month. There are 2 lines on the account. If I port my cell phone number to Verizon, am I going to be charged any amount or will anything happen to the other line on the AT&T account? I tried calling them but the call center is not open on weekends, and I was going to get a phone today since mine is officially dead.