We have a client on version 12 of 3cx, using all T41ps. They have some phones that are showing 20-100 voicemails and when they hit the voicemail button it shows 0. I have them all on the 3cx recommended firmware. They are also using the windows SBC to connect to their 3cx server in our datacenter. I also changed a few to STUN and it seems to still occur.