How do you unlock a t mobile Samsung Galaxy?

The easiest way to do this, without loosing your contacts etc is to call your service provider and request the PUK code, or; You can take the phone in, they should unlock it without a charge (they want you calling out to burn those minutes), or; You can do a hard reset on the phone, WARNING: this will erase EVERYTHING on your phone - it will still work (it knows your number etc) but you will loose settings, contacts, ring tones, etc.