Regular ad-hoc works with players in close proximity. There is a free PS3 application called ad-hoc party that can be used to connect to other players over the internet. You download and install ad-hoc party on your PS3 and launch it. Your PS3 has to be connected to the internet via a cable. It needs its wireless available for the PSP to connect to. You find a room with other people playing the game you want to play on your PSP and then you all connect and play as if you were in close proximity.
Now, just so you understand, ad-hoc party will NOT work while PSN is down.