I can't find anywhere to update this. When I first got my Lumia 920 it kept asking for my visual voicemail password. When I finally got that I accidentally entered it when it asked me for my default voicemail phone number which it also kept prompting me for. This is the number the phone dials when you press and hold 1 or click on the voicemail button to call (before visual voicemail is turned on). So I put in the 4 digit password there instead of the voicemail phone number. Now that it is set, I see no way to set it to the correct voicemail phone number. I can uncheck the Use Default Voicemail Number to enter in the correct one, but it always turns itself back on to the default when I navigate away from the page. I even tried completely resetting the phone and it is still there. That tells me it was written somewhere deeper than the regular settings options. I find it incredibly annoying that AT&T did not set this by default when they setup these phones. If anyone has any ideas please let me know.