Finally 3CX client is on Windows Phone! The app can be downloaded from: https://www.microsoft.com/en-us/store/apps/3cx-phone/9nblggh1nj7b I wanted to report my issues to help 3CX to solve these minor issues: I'm testing it on my Lumia 925 running Windows 10 Mobile Insider Preview, my OS version is: 10.0.10166.0 Outgoing calls: The other party hears him/herself. There is a little delay regarding this loop issue. Incoming calls: If the phone is in sleep state (locked), it does not ring at all. Appearance: Eventhough the client is registered to the 3cx server, the app still says registering on screen.