I have been performing some tests around MWI and external Voice Mail Systems (although I am sure the same issue as described below is also probably the same on unity - I have performed basic tests).
Basically if you have an extension mobility user NOT logged into a phone and their profile provides no features (such as a call forward no answer) that would cause the EM DN to be in the routing table, then when an MWI comes from QSIG or from MWI on/off DN in CCM the MWI is not registered at the CCM as CCM doesnt "know" about that DN at that time. This means when the EM user logs on there is no MWI set, although message waiting. Point makes sense?
Corrected by various methods, including CFWD N/A on the EM Profile.
Anyone else seen this, or comment on correct operation, or infact other better ways of avoiding?
For info version tested on 4.1(3)sr4d with 2000.4.2sr12.