I work for another carrier but depending on how the other carriers work, its usually one of the following:
all 0s (0000 or 000000) , or the last 4 of your phone number, or the zip code it was shipped to when you purchased it. Thats for my provider anyway. try these and let me know, otherwise I can ask some fellow techs. Have you tried calling your provider for the master subsidy lock code (MSL)? It might be wanting that. Otherwise, you can usually take the phone to a service and rrepair center to have the software reloaded if all else fails.

I was messing around with settings, and i believe I went to phone settings. I don't remember the exact name of the setting, but it had 2 options; NAM1 and NAM2. Just wanting to see what it was, i clicked on NAM2. Immediately, my phone restarted. Just like when I had first bought it, it asked me to press send to activate my phone. However, when I pressed send it asked for the phone lock code. I had made one previously to apply whenever the phone was turned on, but when I punched in the 4 digit code, it said it was incorrect. At this point, i'm stuck at the home screen with a locked phone, and I don't know why my password changed, or what it changed to. Please help in any way possible, because at this point i'm so desperate that i'm trying to unlock it going one by one from 0000-9999 . I have a verizon wireless Samsung Reality (model: SCH-U820), if that helps. Please respond soon!