I have this weird issue... I was sitting next to one of my Cisco phones and the LED message indicator came on. The phone did not ring and neither did any of the others, but a message appeared.
I checked on my settings as I have an after hours ring group set up, it was not the problem but I noticed my app memory was at 86%. This is very abnormal for my system as it normally sits at around 25%.
After a reboot, everything returns to normal, phones ring and I can use it ok. If I leave it and watch it, I can watch the App Memory increase in size until the system gets to about 85% and all calls go direct to voicemail again.
I have made no changes to the system, but installing the normal updates via Module Admin.
FreePBX Framework is 184.108.40.206
Asterisk Ver 220.127.116.11
All modules up to date.