The SIM slot is gone, since it's not a GSM phone. That frees up a bunch of real estate on the PC Board. Did Apple move the WiFi antenna (and probably also the GPS antenna) to the PC Board, under the rear glass? I think so.
In their FCC filing, Apple describes the WiFi antenna as a "PIFA". This stands for Planar Inverted-F Antenna. I would never describe the "frame" antenna using those terms. So, this seems to support the theory. Further, the photos (thanks to Arstechnica) of the new Verizon iPhone show elimination of the frame gap on top (which was the WiFi and GPS antenna) and creation of new gaps on the sides.
Is the new iPhone using antenna diversity (two antennas in the frame with switching between them) to compensate for hand effects? Possibly.
(thanks to Greg Keizer of Computer World for sending me the link to the photos.)