iPhone 3Gs Unlock - Keeps Going back To Balance Message

[Insane225]

I'm trying to unlock/hacktivate my iphone 3gs. i have a at&t sim card for it, and I had put minutes on it and drained them. Now, every time I get service trying to unlock or hacktivate, i dial a number and a automatic message informs me that I don't have enough minutes to make the call. So I obviously get service, but it keeps wanting me to refill my minutes instead of making the phone call. Help please? I've tried restoring the phone, along with deactivating in the process, but it still asks me to refill my minutes everytime I get service trying to unlock.

[Insane225]

Can I unlock while still under contract? I looked up my IMEI info and it says I'm under "contract" until April even though its a pre-paid GoPhone.