I have Unity 4.2 integrated with a Nortel Option 11 pbx via PIMG boxes. When i have Unity setting message waiting, it turns on the message waiting lamp (the red triangle) on phones with that lamp. However meridian mail also puts an envelope lights a button when there's a message as well as the lamp. Is there any way to turn that on with my integration -- something i can get the nortel folks to program on their side to make those icons work again? for those people with multiple numbers on their phone, it was something that they used to see which line had voicemail. And there are still some older sets around that don't even have a message lamp -- they only have those icons.
I have worked with Nortel systems for many years and I am pretty sure that this is a MWK Key. For example if the Voicemail Pilot number is 7000, you would program a key on the Nortel Phone like;
Key X MWK 7000
When a message is left and lights the Red Message waiting lamp it also starts a flashing icon on the MWK button. This key will also Speed dial the VM Pilot # (7000) when the handset is taken off-hook and the MWK button is engaged.
Hope this helps! Not sure if this will work with Unity and the PIMG but it's worth a try.