Well, we know GT PSP has shipped about 1.8m, and sold around 1m on VGC when that sales data was. Given how high their GT 5 Prologue numbers are, it is assumed that Polyphony's sales are including PSN data
So, that probably means it has sold about 500k on PSN, given there are some sitting on shelves
This is where I am getting the numbers from:
http://www.polyphony.co.jp/english/list.html







