Hi Paul,What Jabber 4 Windows version are you running?  Are  your userID and mailID in the same format?  There is a bug starting with  Jabber 9.2.4 with visual voicemail.  Basically if User A call User B  and left User B a message, User B will not be...

We ran into the same issue with one individual user, we were able to resolved it by going to Call Manager and remove the user license capability and re-enable it.