All what I was able to find in the internet was, that Microsoft does not allow applications to run in background on Windows Phone. To be honest, I am wondering why then I am able to receive incoming calls e.g. with Skype or Whatsapp app without running those in foreground on my WP10?
It would be very nice, if somebody can explain this or better, if the Zoiper app for windows phone can be updated and fix this issue. Thanks.