Tracfone is notoriously difficult about unlocking older feature phones. They frequently deny requests because the "system no longer supports generating codes for legacy models." If they deny you, do not argue—move to Method 2 or 3.
After dialing the code, insert a non-Tracfone SIM (e.g., a friend’s T-Mobile SIM). If you see signal bars or "T-Mobile" on the screen, you succeeded. If you see "Invalid SIM," "Enter Unlock Code," or "Network Lock," it failed. samsung sgh-s150g sim unlock