The debate over "unlimited" is not exactly settled. Some of us have been sucking up bandwidth (multi-multi-gigs) with no problems, while others have claimed that they were shown the door and their service terminated after using only a couple of gigs.
My personal _opinion_ is that those using AT&T sims are the loudest about having been throttled / terminated. I haven't seen many T-Mobile sim users making the same complaints... or if they do, usually it is just throttling. Those on the Verizon/Sprint phones... well, I haven't heard anything yet. I'm on the Verizon phone and have yet to be issued a warning.
If I had the time and money, I'd get all 4 service carriers through Straight Talk and test it out.