What type of phones? I have had the same problem with different phones. And it always turned out to be a problem with the programming on the phone web interface. I am not saying that is the problem. But it might be a place to check. Again what type of phones?
Sorry for not responding. I have a mixture of Aastra, Polycom, Snom & soft phones. Although I have defined the users with their extensions, when I check the voicemail button on the main interface, there is a message stating "You don't have an extension number associated with the user" .
So I am not sure where the problem is. Voicemail indicators work in the FOP and the phones properly indicate when they have voicemail, it is just on this interface.