I understand what you're trying to say, but it's not correct. I had the 4 and the 4S, which are both 3G phones. I could always talk and go on the internet, with no speed loss problems. Sometime around November last year I noticed the throttling happening. I called AT&T this year, and they did say they throttle now while on the phone, to cut back bandwidth usage. There are many articles on this from last year, before the 5 came out. It used to work, but AT&T is so scared their network might go down, they choose to do this, and nobody every says anything about it. (Except for a few people on the internet rambling about it.)
This has nothing to do with the LTE chip in the 5. I can use voice and data at the same time, unlike Verizon, it's just AT&T has been throttling the data for the last year or so. Oh, well.....
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http://thesmartphonechamp.com/att-secretly-throttling-their-smartphone-customers-video/