Without knowing what prepaid wireless provider you're using, I can't give you specific direction, or research your exact options for password retrieval. However, here are some general things that are pretty common for prepaid wireless voicemail:
1. The first time you call into your voicemail, it usually prompts you to assign a password (typically 4-digits), so try to think back to remember if you went through this step.
2. The default password that many prepaid providers assign is the last four digits of you phone number. You can also try 1234 or the year you bought you phone (ex. 2009).
3. Most carriers allow you to retrieve your password by logging into your account online. Somewhere under account management, there's often an option to reset your voicemail password. Some providers also have this option on the WAP deck on your phone once you sign into your account (on the phone). You may also find an option on the menu system (IVR) when you call the carrier.
4. If all else fails, call your carrier and ask them to help you retrieve/reset your voicemail password.
