Hi Michael,
The mobile Communicate app (which is used for calling... Collaborate only allows chat) uses a WebRTC audio connection over the data networks (either cellular or Wifi) and is therefore more susceptible to data network disruption than "regular" calls outside of the app that use the cellular voice network, making quality comparisons tricky. That's, unfortunately, the nature of the beast. Naturally you often can't control when you need to use the service, especially when receiving calls, but our best guidance would be to try as much as possible to ensure a good data connection. Particularly tricky are when driving (since you're moving between cell towers) or otherwise going in and out of data coverage areas.
For the "not ringing" aspect, you may wish to engage our Care organization to help triage. I know we've adjusted many things already on the Android side to improve incoming calls and we're always looking to improve further.
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Brian Dupuis
Genesys - Employees - Sr. Director, PureCloud UI
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