Share one UMD disk between multiple PSPs in an ad hoc multiplayer WiFi game

You've just bought a brand new PSP and so has your best friend. You are both eager to play head-to-head, using the PSP's wireless gaming capabilities. Unfortunately, you and your friend have differing tastes in games and, as a result, you don't have two copies of any one game between the both of you. Before you run out to rent or buy a duplicate game from your combined lists, try this little method to trick your PlayStation Portables into thinking that you have two copies of your game.

Shortly after the North American release of the PSP, several different sites and online forums began simultaneously reporting that people could play multiplayer ad hoc games among multiple Playstation Portables using only one UMD disk. Here's the basic procedure:

1. Load up an ad hoc multiplayer game on your PSP.
2. Eject the UMD disk.
3. The PSP will ask "Are you sure you want to quit this game?" Quickly select No and hit the X button.
4. Hand the disk to your friend.
5. Your friend puts the UMD disk in her PSP, loads up the game, and connects to the ad hoc multiplayer game you started.
6. Now, either both PSPs will freeze (if this happens, proceed to the next set of steps) or you both will start playing.

Alternately, you can at this point start again from step 2 to invite yet another friend to play.

If both PSPs froze at step 6, then it's time to troubleshoot the swap by doing some more swapping:

1. Your friend ejects the UMD disk and selects not to quit the game.
2. You put the UMD disk back in your PSP.
3. You both start playing. If, yet again, both PSPs freeze at this point, return to step 1 but reverse who gets the disk. Rinse, repeat.

Unfortunately, this trick only works in certain games, and can be slightly different depending on the game you are using. It's mostly a matter of timing, trial, and error.

To give you an idea of how it works, I'm going to walk you through sharing one Tony Hawk's Underground 2 Remix UMD between two PSPs.