Gophone sim card in a Cingular postpay phone

I own a Cingular GoPhone and would really like to get a new phone. My friend is buying a new phone for his regular service Cingular account, and has offered to give me his 'old' phone (using the term loosely, its only 9 months old). My question is, will my SIM card work in the phone without it being unlocked?

are you kidding me? 31 people looked at this thread and not even one can give me a simple yes or no?