GBA emulator for NDS flash carts?

[Jelster64]

What you guys maybe don't understand, is that emulating isn't the only option to play GBA games on the R4. Converting is also possible. Don't ask me how to DLDI patch the game, but with the name NDStation you can come far. It converts GBA roms to NDS roms.

[hadeki]

The Supercard DSTWO has a built-in GBA emulator, so... it's completely possible.
I'm not sure if it's possible for the R4 though.

[lolo64]

you can run GBA games on your DS using slot-1, but you'll need a Supercard DStwo, on sale for about 45-70$.
I know this is expensive, but the flash card is high-performance (I have one) an is able to run on ds, dslite, dsi,
dsi xl and 3ds. it can run DS Games, SNES games, and, of course, GBA games.They run very good!!!
here's the link to the official website:
http://eng.supercard.sc/manual/dstwo/
and here's the link to the review, by GBAtemp
http://gbatemp.net/t232281-supercard-dstwo-review

hope this will help you!!!