We recently deployed around 20 Samsung Galaxy Xcover for use with our new 3CX phone system, and they have been randomly unable to receive calls even after re-doing the entire Firebase configuration and checking twice that everything should be running fine. "no network" issue (while phone is running over reliable 4G mobile access) phone that doesn't ring at all, or does so a minute later (probably when finally acknowledging the firebase push) touchscreen accepting input from users' ear while on a call (what is the proximity sensor option for, really ?) application not restarting properly when asked to quit or quit without push application not coming to front when call is received on some phones (only the notification appears) calls take one to several seconds to be connected when touching the accept button bluetooth headsets have audio and microphone routing issues, not working at all in most cases we tried a variety of solutions including switching from wifi to 4G, removing the lockscreen pattern, automating an application restart every minute but none worked reliably. all the phones are running the same official Samsung Android build, with all Samsung system apps disabled via Gsuite admin (ensuring a nearly pure Android OS), with the same lack of restrictions. Please take a look at Zoiper for something that works and take example. We are extremely disappointed in this system, given that we switched to those smartphones because our old Aastra DECTs "have not been tested" by 3CX and thus are "incompatible". We would also appreciate the application to be allowed for install on Chromebooks, since it is still locked out on the Play Store. I am available for any inquiry and/or test on our deployment, before we switch back to the reliable SIP/DECT solution we had before.