AFKIM (Away From the Keyboard Instant Messenger) is a multi-protocol instant messenger application for the PSP. It supports all the major IM protocols, including AIM, ICQ, MSN, Google Talk and Yahoo!
AFKIM also includes a built-in keyboard that is much easier to use than Sony's keyboard.
You can grab the updated version of AFKIM from the download link below, which includes the source code and versions of the software appropriate for firmwares 1.50 and 3x. Check out the readme file before you jump in and install AFKIM for optimum results.