IGN), the handheld game has you taking up arms as the film's blue-skinned Na'vi aliens after their village is destroyed by the human RDA force. Based on the plot similarities, it's likely that the PSP game is based on the Wii version and not the PS3/360 game.
Like Assassin's Creed: Bloodlines, the two PlayStation Avatar games will be able to communicate with each other. One feature revealed so far is the ability to transfer "Effort Points" from the PSP game to the PS3. That's not immediately exciting stuff, but we're hoping that more interesting connectivity features will be revealed at a later stage.