I don't think the PAL argument comes into a DS - AFAIK all handhelds are region free.
Also, as with Game Boy games, some games that require both players to have a Nintendo DS game card for multiplayer play will not work together if the games are from different regions (e.g. a Japanese Nintendo DS game may not work with a North American Nintendo DS game, though some titles, such as Mario Kart DS, are mutually compatible).