Unlocked Phone Help With Sim Card?

Hi There, Question, I Want To Buy A Unlocked Cingular Phone I Saw.. But I Have Tmobile Service And A Tmobile Sim Card.. Do You Know If I Insert My Tmobile Sim Into This Phone If It Will Be Tmobile Specific? I Heard There Was Something That Had To Be Done To The Phone To Make Sure The Tmobile Preferences Are Put In For Tzones, Tmobile Welcome Screen, Messaging Systems, Etc?
Can Anyone Help? Thanks

stop posting the same questions in different forums.

I didn't catch in of the other posts but a phone model would be nice, there are several ways to fix this problem but we would first need to know the make and model