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Weird, I used 7gb of data on iPhone 5s and was not throttled..

AT&T doesn't always thottle unlimited users -- but no one really knows under what circumstances they do. It's assumed that people in areas where there are fewer users hitting the towers aren't always throttled. However, AT&T hasn't said anything about it.
 
MAIN POINT
Nowhere in the agreement is there a definition of the word "unlimited" that trims it to their particular slant of "unlimited but lower speed" and the purchaser at that point has every reason the expect the common use of the term.

As you would expect with any company that has a stable of salaried lawyers, they'll have covered their bases.

http://www.att.com/shop/en/legalterms.html?toskey=wirelessCustomerAgreement
Within Section 6.2:
Unlimited Data Customers. If you are a grandfathered AT&T unlimited plan data service customer, you agree that “unlimited” means you pay a fixed monthly charge for wireless data service regardless of how much data you use. You further agree that “unlimited” does not mean that you can use AT&T’s wireless data service in any way that you choose or for any prohibited activities, and that if you use your unlimited data plan in any manner that is prohibited, AT&T can limit, restrict, suspend or terminate your data service or switch you to a tiered data plan.
 
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