Hi Sant
You just need to tell visual voicemail about the voicemail huntgroup. You programme the Visual Voicemail Huntgroup in the voicemail form.
Goto a user -> Voicemail tab -> Visual Voicemail Huntgroup, pop in the voicemail huntgroup (usually 5555) save.
You can range programme this for all mailboxes via the voicemail form one tested working.
That should do the trick.