Here's what i've noticed as a benefit to the merger.
I live in Atlanta, and about a week ago, a friend and I took a road trip to Florida. There was probably an hour and a half stretch where I roamed onto T-mobile's network. Apparently, Cingular and T-Mobile have a mutual agreement to roam onto one another's networks for no additional charge. All calls that I made out of this area were not charged a premium, and fell within my unlimited roaming plan. At&t apparently didn't have this agreement in place, and had I been there say 6 months ago, it could have been a completely different story.
I think rollover's a great feature to add, but i don't like the cap on the night and weekend minutes. The anytime minutes aren't as good for the money, so I'm pleased to be locked into my contract at this time. Who knows, their packages might get better for at&t merger customers. We can only wait and see!