Grandstream BT101 and MWI light

I have had a reasonably good look round this forum but cannot find out what I want to know.

I have my asterisk server intercepting my analogue line, and also I have another two geographic VOIP lines via IAX from a third party supplier.

Now here is the deal; I want to be able to get the MWI light to come on when someone leaves a message on the server for any of the lines, VOIP or PSTN. When the analogue line rings, all of the extensions on the house are set to ring. I have to log into the mail box in order to retreive my messages. I also have an ATA186 for my old DECT cordless handsets, and the wife has got the monk on about it not doing a stuttered dial tone like the BT answer service does. I understand the ATA’s offer this function for MWI.

Is there a way to do this in the dialplan? Any pointers would be really appreciated, and I could probably work from there. Asterisk is great, I love it!