In my opinion, this is a really bad idea.
First of all, the Game Boy Advance is not a system capable of handling the needs of a game such a Grand Theft Auto. Second, Nintendo is a game company that's aiming in a younger crowd than the rest of the game companies. Especially Game Boy is for children to pre-teens. I, for one, bought Game Boy Color at the age of 10. Consequently, Game Boy Advance cannot host even a pixel of a Grand Theft Auto game.
On the other hand, PSP, a new state-of-the-art handheld system, with excellent graphics, digital sound and net play is an ideal host of a GTA game.
That's what I think... Those who agree with me, those who don't, state your ideas below.