To quote from http://www.engadget.com/2006/03/24/psp-keyboard-and-cellphone-attachments-on-uspto/:
So if you recall, way back at E3 2004 when Sony was showing off the PlayStation Portable for the first time in the US, they were also generating some buzz with translucent keyboard and cellphone attachments. Of course, those never materialized -- but they have in fact finally shown up online, albeit at the USPTO.

In two filings dated November 10, 2004 (and made public in late February 2006 and only three days ago, respectively), a gaggle of Sony designers submitted applications for both "ornamental design[s]" for a keyboard and phone add-on for the PSP -- and trust us, the patent filings couldn't have been much less verbose. So will we ever see these things get manufactured and released? Eh, even though Sony's launched some unexpected PSP accessories recently, we'd assume the phone attachment won't ever take off. However, Izumi Kawanishi has made it no secret that he wants email on the PSP, and a keyboard would be quite a nicety if that's in the cards.