updated 12:52 pm EDT, Mon July 21, 2014
Rough edges disappear
New photos show what is believed to be a rear shell for the iPhone 6 from a later stage of manufacturing. The shell notably has an iPad-style inlaid Apple logo, and a smoother overall appearance, unlike some earlier leaked shells. The reason for the switch to an inlaid logo is unclear, but it's speculated that Apple may want it to light up, possibly to serve as a notification light, something present on many non-Apple smartphones.
Another possibility is that one or more antennas will be located behind the logo so that Apple can use metal for the rest of the shell. The iPhone 6 may potentially use some decorative glass and/or plastic, like the 5s, but reports have so far hinted that Apple is moving iPhone design closer to the iPad, which is all-metal except where absolutely necessary.