Both my iPhone & LTE equipped Android are on lines with grandfathered unlimited plans at AT&T.
I've been using a massive amount of data via LTE, it's easy to do. Plus I do use my Android somewhat more than my iP4S.
I've never been throttled (not saying it's not possible) and the price has not increased.
Despite all the haters that pile on AT&T, I've had nothing but great service for many years.