It appears that a new installlment of Sonic is appearing on the GBA. Sonic Advance 3 is to be out this summer....but what I saw from the pictures on the link I've posted below....has led me to infer that it is more of a SonicHeroes for GBA....considering the Boss Rooms, mulitplayer, and dialogue between characters.....

I guess we'll see....
http://media.gameboy.ign.com/media/5...63/imgs_1.html