You all are VERY LATE TO THE TABLE on this!!! AT&T has been throttling data speeds during calls for a couple years now. I have noticed its a tad bit faster than before. I can get about 1.5mb down, but upload is always 0.0mb.
I am betting once they go VoLTE, they'll still throttle, just not as much. What makes it so miserable is that the pings are in the 400s. Hang up and you get great performance.
T-Mobile DOES NOT DO THIS IF ANYONE IS WONDERING!
Past Devices: Samsung Galaxy S2, iphone 4S, S3, iphone5, Note, Note 2, iphone 5S, Note 3 (N900T) Current: Galaxy S4 32GB (i337) w/ MDL firmware