We have a customer with CM 7.1.3 and Unity Connection 7.1.3 with new SIP 8961 phones since they liked Visual Voicemail option it is turned on globally and TUI is turned off. Everything works fine and customer and end users really like this except one issue, whenever they go to Visual VM to check messages and exit from it and when the phone goes off hook there is no dial tone at all but if you dial the numbers the call will go through fine and same incoming call works fine too.
If you reset the phone you will get the dial tone as normal but as soon as user checks VM through Visual VM then it behaves the same way no dial tone from that point. It is weird since it is all new to me really don't know where to start troubleshooting.
Thanks for your help.