GBA emulators work amazingly on my phone. It can get a bit fussy if you have an iPhone, but the controls have always been really easy to work in my experience. When I want to relive my old Pokemon days, I just throw a rom on my phone and play it casually on the bus. Much preferable to digging around in the closet for my old Gameboy.
Oh damn had no idea that was actually possible! I have an Iphone 4s can I do it too? How exactly do is set it up?
It can be a little hard depending on how you want to do it (with or without jailbreak). My phone isn't jailbroken but I have GBA4iOS, and it runs perfectly.