Were you able to solve this issue? I am facing the same problem and I can not find any relevant document. I mean the voicemails should appear here like they do on Jabber for Windows, right? Even in jabber for iphone this works fine.
In the Jabber for iPad applications under settings if you scroll to the bottom there is a section labeled "Unified Communications Manager" the first option shoudl be "Voicemail Pilot Number". You need to enter the pilot number for your voicemail system there