Voicemail Password

I gave my wife my 32GB 3GS (I upgraded to an iPhone 4) to replace her 16GB 3G. Neither of us has ever used a password to access our voicemail but after updating her old phone, transferring all of the photos off of it, making sure her contacts, music and apps were updated and syncing the phone, then restoring the 3GS from her back-up, a message keeps popping up asking for a Voicemail Password. Short of doing a Restore of the 3GS and then doing a resync, how can I fix this? If I have to do a restore, her back-up will still be available to resync to correct?

Thanks!

JMB