Play Multi Player With One UMD On Sony PSPs
Playing the Multi-player games with one UMD on your Sony PSPs is possible, follow the simple steps below
Start up an ad hoc multiplayer game and set the time for unlimited. Do this on the first PSP.
Eject the UMD disc and choose NO when it asks if you would like to quit, on the first PSP.
Put the UMD in another PSP and start multiplayer gaming with your friends!
Repeat previous 2 steps for as many players as you want in the game.
The PSP manual states that removing any kind of UMD while it's in use, can cause the PSP to freeze, malfunction, or even break your PSP. (see external links)
If you want a safer way of doing this, download demos with AD-HOC feature from the Playstation Store.
This method only works on some titles.
Only attempt this on a original psp. PSP slim and lite and PSP 3000 are updated hardware and won't let you play without a disc.