People have mentioned the video conferencing several times (if it's even allowed over 3G and not wifi only), so one thing that I have wondered is what if Apple has asked AT&T to include unlimited video conferencing in the iPhone data plan, since it will be one of the stand-out features of the iPhone 4th gen? And as a compromise, AT&T told Apple that their network wouldn't be able to handle unlimited video chat PLUS unlimited data (non-video chat data), so they (AT&T) said that to allow unlimited video chat, they would HAVE to cap the other data usage at 2Gb, and grandfather the existing iPhone owners into their old plan so they don't revolt? This agreement would satisfy both Apple and AT&T, as Apple and Jobs still would get to tout their new video chat feature that I'm sure they are going to want to advertise heavily as being something that the competition really doesn't have at this point (except for the Evo), and AT&T doesn't have to worry with the possible situation of having all these iPhones with unlimited video chat (which would be data), PLUS unlimited other data (web browsing, app downloads, streaming, etc).
So in a nutshell, what I'm saying is what if we find out Monday that the 4th gen iPhone will have unlimited video chat on the new plans, but the data (non-video chat data) will be capped at the proposed caps? This may be why we haven't heard a peep out of Apple about this.
And if the above is true, then anyone upgrading to the 4th gen iPhone but grandfathering their old unlimited plan wouldn't get the video chat feature, since the feature code may be attached to the "new" iPhone plans. This might be how AT&T is going to try to "strongarm" all of us wanting to keep the old plan but get the new phone into going with one of the newer, capped plans.