A Mobile Phone/Pen

It's a phone that you write with. No wait - it's a pen that's as big as a cell phone.

"Siemens goes small with the new PenPhone, the first ever tri-band mobile phone housed in the unusual shape of a pen and offering all the features of a standard mobile phone. The 140mm (5.6") long PenPhone recognizes handwriting for dialing numbers and writing text messages directly into the mobile phone -- no matter what surface you write on."

...providing a perfect illustration of the saying "Just because you can do something doesn't mean you should."