According to IGN, the PlayStation Network will receive enhanced capabilities this fall with the PSP in mind. All models are of course supported.
First off, the PlayStation Store will be accessible directly from a PSP. You can download the demo for Phantasy Star Portable (and other things) directly.* This is as opposed to using a PS3 or PC.
Most excitingly, there will be infrastructure capabilities for PS3 owners. Many games that currently only support ad-hoc multiplayer will be able to be played online (without the use of a certain unofficial application). Users will not only be able to find games, but also be able to take advantage of text and voice chat. Monster Hunter Portable 2nd G is the first announced title to be supported. I imagine there is also room for a title that has cleared 600k copies (and is currently the 5th best selling PSP game in Japan).
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