I think I have figured out what all this means.
I think maybe:
A. Apple did this knowing it would be a way for the masses to show their discontent for it. Knowing that if the carriers do charge, it looks bad on the carriers and not Apple.
B. Apple may prepay for x amount of FaceTime calls and wanted to get a feel for the response FaceTime over 3g would have.
C. ATT, knowing the iPhone 4 launch day people are coming up on the end of their contracts (and there were millions of them - remember this was pre-Verizon) and now that several regional and prepaid carriers now exist (and hopefully T-Mobile will be added), wanted to gauge the outrage. I don't think FaceTime was all that spectacular, neat yes, but it wasn't a super high feature on the list. I think maybe ATT thought this would be a ho-hum addition but wanted to see how people reacted.
Just my thoughts, ATT doesn't have the monopoly they once had, many more choices now than a year ago. I'm not saying they "care", but clearly charging gives Sprint and Verizon and x carriers a horn to toot and makes for bad publicity.
And, I laugh at this but,a couple of my co-workers are convinced Apple will buy T-Mobile's US operations and be the network they want the iPhone to be on. I remember talk about this back in 2000 or so. I just don't see Apple getting into the network business.