This happens to me every once in a while, not often, but it's easily fixed by leaving myself a message and then picking it up. I always assumed that the MWI signal was not a discrete code, but a toggle. Somewhere along the line, the signal is missed, and it won't correct itself until another signal is sent. Is this incorrect? Does the server send (and more importantly, does the phone "hear") a discrete "ON" or "OFF," or is it a toggle? I don't know the answer, I'm just asking.