visual voice mail not available

Reset network settings has fixed this for me in the past.

I just went through this... (my new iphone worked flawlessly before the 3.1 update). I tried with both Apple and ATT to deal with this issue for a whole day... (I figured since it was a voicemail issue it was an ATT problem, but turns out it was 3.1).

I tried to back up and restore several times that day, but same problem, visual voice mail disappeared once I was back up and running... finally an Apple support person had me back up and restore (but this time configure as a new phone... and this is the important part... right click on the iPhone icon where it appears on the left hand side and choose SYNC... not Restore. (Didn't even know this existed). This will sync your Contacts and iCal but nothing else... no settings.. (Apps and email settings were brought over on my first sync automatically, but no emails were imported). This is the only thing that worked for me after several tries. You will have to set up everything on your phone again the way you had it (System settings, etc)... it will be like a new phone.

SInce all my emails exist on my MacBook Pro, it wasn't a big deal for me, since I didn't loose anything but a lot of time.