Most of the people that had them unlocked have sold the phone already. It's the people that bought used phones that will reap the reward of all of a sudden not having their phone work when AT&T relocks them. Add this to list of reasons I would never buy a used phone. There can be enough issues getting new phones.
For those that unlocked to go overseas, maybe they will still work there, not sure. But if you still have your phone, once it's paid for, get it unlocked for free legitimately. It was suspected many times that these pay to unlock services were doing so by fraudulent means.
When will FCC put their foot down and end this locking none sense once and for all with all carriers. This is 2015, I don't buy my television from Comcast, or Dish or AT&T. shouldn't buy my phone from AT&T, Verizon, T-Mobile, or Sprint either. One of these days we will finally get an all band world phone and not confuse consumers with dozen different models.