I didn't know "1" dialed voicemail, and just created a shortcut for "v" to dial it. Go to "call log", hit your wheel, and select "view speed dial list". Set it to whatever you want. I guess "1" would be "w". My brain understands "v" for voicemail better
I had the same problem after upgrading to 4.02. I found the solution on another forum.
1. Go to the phone icon and open up the Speed Dial List.
2. Find the "W" on the list, highlight and then choose "delete" from the menu. Even if it is blank, do this.
3. Reboot by removing the battery for about 60 seconds.