From what I know its still to be announced. It was supposed to come out a couple years ago but there has been a mountain of delays. It probably wont be till 2009.
Gran Turismo 4 Mobile Cancelled?
The handheld version may officially be vaporware
January 11, 2008 - Sony announced way back in 2004 it was prepping a PSP version of Gran Turismo 4 for on-the-go racing. It was supposed to be an "exact replica" of the PlayStation 2 game. But we haven't received an update on the title since mid-2006, when series producer Kazunori Yamauchi told Famitsu that it was still on the way.
It looks like Gran Turismo 4 Mobile may not ever cross the finish line, though, as an IGN staff member just received a call from GameStop bearing bad news. The retailer says pre-orders of the game have been cancelled -- because the game has been cancelled. By the vendor, apparently.
As of this writing, Sony representatives could not be reached for comment. If the news is true we can't say we're entirely surprised. Four years is a long time for a direct port to be in development, and two years is an eternity to go without a status update.
it was not cancelled jsut put off for a while and renamed, gran turismo mobile will be out launch day of the psp go 10/1/09, it will ahve many of the same tracks as gt4, and a few more, and its on game, not a edited version of another GT game
