I'm guessing all the antennas are inside the top and bottom of the phone where it is glass. The middle back plate is aluminum.
I don't think the frame is going to be the GSM, UMTS, etc. antennas anymore. If they are, then of course it won't touch the aluminum backing, and the glass top and bottom will just cover the internal WiFi, Bluetooth, GPS, etc. antenna. As it is now, the glass is covering an internal antenna. Yes, that is (likely) a black antenna just under the top of the back glass plate (not visible) in the iPhone 4 and 4S.
I also believe, along with many others that, again, there won't be a teardrop design. It may look cool, but I want a battery that'll last more than 2 hours in there. (A teardrop design seems to take out 30%-50% of the volume, meaning the battery would be less than half the current size.)