Can I unlock a registered phone?

I wrote before about this. I got a Net10 Samsung S390G phone online. I didn't realize it was a Net10 phone until I received it but I really prefer it under my Tracfone account. As soon as I put the Net10 SIM back in the phone was registered to Net10. There are a lot of unlock instructions on the web for that phone. Can I trust any of them and can I even unlock a phone that has already been registered? Thanks.

via Forums de téléphone cellulaire (en français) http://cellphoneforums.net/fr/general-cell-phone-forum/t365409-can-i-unlock-a-registered-phone.html