This was not true of AT&T when Verizon announced this. Not sure if the policy has changed in recent months, but I do not believe you lose unlimited by getting a new subsidized phone on AT&T.
Sent from my iPhone using SatelliteGuys
That's a nice bonus for AT&T customers. As much as I liked the security of unlimited data on Verizon I wasn't willing to pay over $700 for my 32GB iPhone 5.