"When I dial my own number, from that phone, all I get is a busy signal. Any other ideas? (Nokia Lumia 920 with WP 8.1) I realize you posted your answer almost 3 years ago, but I hope you see this."
What you need to do is call your voicemail, which is to press and hold down the 1 key on your phone pad, then follow prompts Admin, Change options, change/set password. I did a very simple 4 digit number, entered it when the Visual Voicemail password prompt came up, and viola! No more password requests prompts! So far...
BTW I have a Nokia Lumia 635 with Windows 8.1 and what I really HATE is that you have to go through three screens just to dial a number. Woe betide the moment I need to dial 911 - without my glasses!