The iPhone 6 may indeed have a partial glass back like the iPhone 5s, says Japan's
Nikkei. Most
panel leaks have shown all-metal backs with lines near the top and bottom. It's now suggested, though, that those lines are simply markers for where the glass will go. The iPhone 5s has glass "windows" along the top and bottom of its back to allow radio signals to pass through.
Nikkei also
claims that the back's Apple logo will be cut out of the aluminum, rather than engraved, and that the phone will use a curved display. The last point may raise doubts, since the majority of recent reports have indicated a flat screen, or at least made no reference to curves.