Originally Posted by
Jim_in_VA you can if you have Advanced Calling (VoLTE) turned on
This, but if you get outside an LTE signal, that will go away. In older phones, there were two radios. One for voice, one for data. This is what allowed you to talk and surf at the same time, because you had a separate radio for each type of signal.
In the G4 and most newer phones, there's only one radio. Using traditional methods, it can only do talk or data. With LTE and advanced calling, the call is handled as a mobile data stream, similar to using an app like Skype to make a VOIP call. Since the call is acting as mobile data, the radio stays in data mode and can keep transmitting your internet stuff.