A little over a decade ago now, back when the Sony PSP was current, there was a neat little homebrew IM client called AFKIM. It used bitlbee to connect to various IM services (AIM, GTalk, MSN, etc.) and worked pretty well for something running on a PSP.

The keyboard, though, was great:

http://localhost.geek.nz/afkim/docs/usingafkim.html

It's a 3x3 matrix. You use the analog stick to pick a square, then hit one of the face buttons to enter a character. Left and right shoulder buttons shifted the keyboard to uppercase, numbers, specials, etc.

IIRC it was a Lua module that any PSP homebrewer could drop into their application for a pretty decent OSK.