After upgrading my iPhone to iOS 4.2.1, I noticed that visual voicemail wasn’t working. The iPhone app kept asking for password. You can change

and reset your iPhone voicemail password through att support. Note that for your own security, make sure to change your password after initially setting up your voicemail. You feel like to know the procedure for reset iPhone voicemail password

1. Call 611 or 800-331-0500
2. Press 1 to use existing number, or enter the wireless number starting with area code
3. Press the 3 key to get help with voicemail
4. Press the 3 key to reset your Voice Mail password
5. Enter your Billing Zip code for the account
6. A temporary password will be sent via SMS to your wireless handset
7. Access voicemail with this temporary password

If you have never set up a password for your voicemail on your phone, your password should be your 10-digit phone number