For Motorolas, I would suggest going into Settings, Advanced, and there are two options: Master reset, and Master Clear... do both and you should be in good shape. (those options might also be in a menu called initial setup, that was like two phones ago)
OH ya. sorry about that. If it's six digits...pretty sure it is 000000. If it's four digits, it might be 1234, 0000, or the last 4 of your phone number. Try that.