So if you are on T-mobile and you are having problems with your voicemail then this may help
One thing I would try is turning off voicemail, waiting an hour or so then turning it back on by dialing 150 and follow the automated prompts:
2 – main menu
4 – tech support
2 – other
1 – help with voicemail
then turn off / turn on
There is another option that you could try first that will resend the settings to the phone.
Once you have sorted that you may want to change the number of rings before voicemail activates
dial this in your mobile, **61*Your.Mailbox.Number**30# The ending **30# is for 30 seconds (can be from 5 – 30)