Sometimes you will experience no audio on the Groundwire software phone application on your mobile / cellular phone. This is often caused by broken carrier grade NAT when attempting to switch between IPv4 and IPv6 addresses.
To resolve this simply follow the steps below:
1) Tap on the Three Dots at the top right.
2) Tap on Preferences
3) Tap on Network (under Network and Security)
4) Scroll to the very bottom of the page and turn on “Use Legacy RTP Layer”
The next call you make should give you two way audio.