A series of patents filed by Sony Computer Entertainment America in October 2009, but not published until the 25th of November 2010, supports the on-going rumors that Sony is building a PSP2 with a touch pad on the back of the devices. In total, seven patents were filed covering not only the touch pad but some rather broad ideas that seem to describe multi-touch and a dynamic UI. Electronista has the full story.
To quote Electronista, the patents "make reference to having a touch surface distinct from the screen that could be used to steer content without interruption" which, when you think about it, is what the track pad on any laptop does. The only thing somewhat unique about this implementation is that the track pad is on the back of the device (the Motorola Backflip Android phone also has a track pad on the back). Since these patents were filed by SCEA (Sony's gaming division) it's a good guess they refer to the PSP2, but that doesn't mean that the same feature is out of the question for a Sony Playstation phone. In either case, exactly what interactions will be performed via the rear touch pad remain to be seen. Without adding a cursor to the display it couldn't be anything very precise (in other words, you wouldn't want to have to tap on a specific spot on the UI), but scrolling through menus, swiping to select items in inventory or panning around a map all seem like viable touch-enabled gaming UI interactions that you can do 'blind.' In shooter games you'll often have a gun reticle (essentially a cursor) anyway so aiming could be done via a rear pad. It seems almost a given that the (thus far unannounced) PSP2 will arrive in 2011 so Sony will have to show its hand soon in order to start building market awareness. As for the Playstation Phone, Sony Ericsson France is hosting an event on December 9th that seems very likely to be an announcement of the device, given the familiar Playstation icons on the invitation. Nowhereelse.fr shared details, including a picture of the invite.