http://www.siliconera.com/2011/09/20/playstation-vita-and-psp-know-how-to-talk-to-each-other-in-ad-hoc-mode/

Let’s say you have Monster Hunter Portable 3rd and a friend has the same game installed on PlayStation Vita. Can you play together? The answer is yes. PlayStation Vita can play downloadable PSP games and communicate with PSP for ad-hoc play.

While it isn’t as prevalent in the West, ad-hoc games are quite popular in Japan especially with respect to the multiplayer hunting genre. And if you like the Vita’s OLED screen you can play a digital copy of God Eater Burst on it and be the envy of your Aragami hunting group. Also a plus for Lord of Apocalypse, which Square Enix announced for PSP and PlayStation Vita.

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That's an extremely nice feature, and I imagine it will be especially important in Japan for Monster Hunter players.

This is amazing news!

So can that other portable console that shall remain nameless. I'm just sayin'!!

Super Sayin', actually.

i thought people already knew this ? O_o

It would be strange if it didn't work together. The DS and 3DS can work together fine with the same DS game, so I don't see why the PSP and Vita would be any different. Except for the fact that one version would have to be the downloaded game as the Vita can't use UMD's.

BTW did they actually release MHP3rd as a digital download? I remember when it first released there was no digital version of the game, but I hadn't heard anything since then.

Well it would be rather weird if they didn't work together.