Nokia 6230

Can someone please help me? My moto razr quit working the other day so I was going to start using my nokia 6230 again. When I put my sim card in it say phone restricted enter restriction code. I and my service provider have tried everything and nothing works. My sim is a 3g. I can put my husband's sim in at it will work fine, his is not a 3g sim. My sister has the same exact phone and a 3g sim and her's works fine. Any suggestions?