I am not sure what type of voicemail system. I did fix the issue, however I do not know why.
When I first set his phone up for voicemail, I thought his Ext. was 2236 because of a sticker on the handset, however the handset would not ring for 2236(would get a busy or out of service message). I found his extension was actually be 2242 by using F*0 intercom, leading me to believe the extension was changed at some point.
He was able to get into his voicemail and everything for a week or two, until today because he was locked out.
I went into F983 and reset the password for ext 2242 which did not work, so I deleted the MBOX and tried to re-add, and thats when I made the post.
From what you guys typed, instead of searching for extension 2242 to reset the PW, I searched in directory and found his name and reset the PW( the ext. said it was 2242), and now he is able to get back into his VM. I am not sure whats going on. When I search for the extension 2236 its not valid.