Plan stays identical. They should run through the normal checklist to make sure you want to keep what you have, but I would advise making it known you want to keep unlimited data. When the guy was going over my plan, he asked if I wanted to keep unlimited data (of course I said yes), but he did mention that he was given the option or prompted to switch me to a 4GB promotional data package as he was going through the upgrade steps. He was on top of his stuff and knew to ask, but I could certainly see a less savvy person accepting the promotion without ever mentioning it. Again, they should mention this at the very end before you sign your new agreement, but I wouldn't put it past anyone to oversee this subtle mistake.