Why doesn't my S3 receive calls while working on apps?

[laurencastro]

S3 doesn't receive calls while working on app

Everytime I'm working on an app (whatsapp, facebook, instagram...) my phone doesn't receive calls and seconds later I receive a message saying that someone called. Does anybody knows how I can fix this?

Phone is a Samsung Galaxy S3

 

[Rukbat]

Re: S3 doesn't receive calls while working on app

Run an app like LTE Discovery or SignalCheck Lite and see if you're still connected to the tower when you're running an app.