It comes back after I hang up the call. I just had it stop and not come back 2 times since I installed 901 (had nothing to do with a phone call).It has always been that way. only LTE (4g) allows data and voice to be working the same time. 3g never did.
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Ignore my reply I misunderstood your post. You are saying it goes away and never comes back. That's different.
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For the past two months I havnt noticed that I lose 3g while in a phone call. Dont think its happened before, I think I would have realized it before (but not 100% for sure though).