Siemens HiPath8000 + Asterisk Voicemail + MWI


As PBX I am using a HiPath 8000 (now known as OpenScape Voice). The phones (OpenStage 40) are connected via SIP to the HiPath8000.

On the HiPath8000 I have a SIP Trunk to an Asterisk Server which I am using as Voicemail (working perfectly).

I am just wondering how I can enable MWI on my OpenStage Phones. Due to the fact that the phones are connected via SIP and not TDM the “externnotify” is not working.

Has anyone an Idea or already tried to implement this feature?