How can I restore lost voicemails after iOS 5 update?

I've seen a lot of posts of this sort, but I've been trying to fix this issue for months and I really need some experienced help... When I updated my phone to iOS 5, I received a message saying my phone couldn't be restored because the backup was encrypted--I had neither requested nor set a password for this encryption. The phone now had none of my information on it, notes, texts, voicemail. I panicked, called Apple, and they helped me find a way to restore the notes from files in iTunes, which is a relief because I'm a writer and had a lot of work in there.

However, the phone started asking me for a voicemail password that to my knowledge, I had never set. I tried a few passwords and attempted a few other methods of recovery, all to no avail. So I reset my voicemail password, as all the online literature I could find suggested. However, the "password is incorrect, please enter your password" prompt then no longer showed up. After long deliberation I set up visual voicemail over again, but to my dismay I no longer have any saved messages.

At this point I have lost over a year's worth of text messages and voicemails. Some of these were incredibly important to me. I would love to recover all of it if possible, but I particularly care about the saved voicemails. Some of these were from my girlfriend during a difficult time in our lives and I really need them back. I also lost important texts from my girlfriend, best friend, and siblings, but the most important thing is the voicemails.

Nothing I'm concerned about is more than a year old, but there are around five or six voicemails I need. No, there is no deleted folder from which I can undelete messages, I know how to do that. My phone is not yet jailbroken but I'm not against doing it if it will allow other methods of restoration to be attempted. I do some coding myself and I'm not daunted by the prospect of sifting around in my computer's files and command line, by the way. I still have all the itunes backups, although half of them are still encrypted with an unknown password. I will pretty much try anything to get these messages back.

Does anyone have any suggestions?