According to "publisher sources", Eurogamer are reporting that games for a true successor to the PlayStation Portable - a PSP2, if you will - are already in development.
If correct, this means Sony's second handheld console is, what...a year away? Two at the most? Sounds about right, when you consider the original PSP launched in 2004. Five-to-six years is a healthy lifespan for a handheld.
Still, that's all pie-in-the-sky stuff at the moment. It's for the distant future. Closer to the present is news that, in the meantime, Sony plans another iteration of the current PSP, the PSP-4000. Due for release in late 2009, no other details were mentioned, though with a new PSP on the horizon any changes would surely be minor ones.
PSP-4000 in 2009, PSP2 later [Eurogamer]