Do flashcards work on all DS

Hi do Flash cards work on all ds cos my friend has a ds and i was going to try it on there ds but their ds is a slim model mine is the big old model.
So if i try it on there ds should it work? After i test it out will they still be able to play there games i heard from some where that once you put a flash card in you might not be able to play normale games with the normal game card but that did not sound right to me...

Flashcarts that work on the DS Lite will also work on the original Big DS.The only one that is different is the DSi. The DSi needs special flashcarts to work, and these flashcarts will also work on the DS/DS Lite, but the ones designed for the DS/DSLite only will not work on the DSi.

ok thanks for that much appreciated..

On the DSi though, an Acekard 2i can be used