To explain things a bit better.... There's almost no way to run gba roms fullspeed like in a DS lite. You're only options are:
- Use a flashcart compatible with Wood (R4i Gold for example) and use the gbaemu4ds homebrew. It still got no sound for lots of game and many compatibility issues, but I was surprised to found out that many games run really fast. Their user interface is not exactly friendly too, since it's still in a "experimental" stage
- Use a Supercard DStwo, it has a built-in emulator. Compatibility is way better but it is still not a perfect, don't expect to run every game fullspeed without using frameskip. The DS2 is the best option for playing gba on 3ds but if you want absolutely perfect emulation you will be dissapointed. Many people here consider the DS2 gba emulation good enough though, it's more likely that you will like it too.
- Get an ambassador 3DS, btw I suspect the 3DS can run gba roms without emulation by using some sort of gba mode. Don't quote me on that though. This option most likely allow you to play the games with fullspeed and have minimum glitches. Even with an ambassador 3DS you're still limited to only 10 selected gba games so it's not a very good alternative imo. Nothing stops Nintendo from releasing these and other gba roms to normal 3ds owners but if they'll ever do it, it will take a long time