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 IGN 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 vender, apparently.