said by Bugblndr:I've had that issue a few times. Not sure why it happens but I find switching voip.ms servers solves it everytime for me. For example, switching from toronto.voip.ms to chicago.voip.ms or montreal.voip.ms.
1. Stay away from toronto.voip.ms -- very unstable over the past year. The montreal servers work so much better.
2. Disable the "SIP Tracking/NAT helper" on your router, if it has a way to do so. For my TomatoUSB router, this is on the "Advanced --> Conntrack/Netfilter" screen, near the bottom.