The instructions for unlocking the 7130c are a bit different and have a few nuances that vary from the other phones. I thought it would be helpful to write them here especially for newbs like myself who found out the hard way...
1. Make sure the Cingular SIM card is in the phone.
2. Turn on the phone.
3. Turn off the wireless radio (very important)
4. Turn on multitap... easy way to do this is to go into one of your email accounts and begin to compose a new message. Click the wheel and select multitap.
5. Go to Options>Advanced Options>SIM card
6. Type mepd (hit m key once, e key once, p key twice, d key once)
7. Type mep2 (hit m key once, e key once, p key twice, hit ALT + 2 for the number 2)
8. In the dialogue box type the unlock code.
9. Hit the ENTER key on the keyboard.
10. You should get a message that code was accepted.
11. Reboot by taking battery out waiting 15 seconds and putting it back in.
This should do it...