He may be able to force-choke someone from afar and blow up entire worlds, but Darth Vader can't get a good signal on his (presumably black) iPhone 4.
AT&T has notoriously bad coverage in a few major metropolitan areas, namely San Francisco and the Death Star. Apple's issues with the iPhone 4's external antenna have only made these issues an even bigger deal. Because of this, the Dark Lord of the Sith himself, Darth Vader, finally gave in and called Apple support. We can only assume the employees at the Death Star's Apple Store are happy he didn't schedule a Genius Bar appointment.
Check out the video courtesy of nbcbayarea.com and see how problems with the iPhone 4 plague even the Emperor's right-hand man: