So apparently a patent has just been filed for a PDA with a detachable cellphone. It works like this: The phone sits in a recess behind the PDA. When they're docked, you can transfer contacts from one to the other. When detached, the mobile works like a standard cellie, relying on its own battery.
An idea like this would have been cool maybe 15 years ago (before smartphones came into the picture). Today, I can only see it being (slightly) useful if it's a slim camera attached to a smartphone, so that taking pictures won't suck up my phone's battery life.
Patent Filed for PDA with Detachable Mobile Phone [Mobile Whack]