I think unlocking Tracfones will do you no good. You will not be able to use another carrier's SIM card in the phone. The best way is to get it reflashed/unlocked (Re-programed) so that you can use the T-Mobile or Cingular SIM cards in them. Once you get them reflashed, you will NOT be able to use the Tracfone SIM card in it.
Solution to have your tracfone unlocked/reflashed: http://unlocknokia.byyourcommand.net/viewtopic.php?t=4373