MeBoy brings back some memories. I used it to catch so many Pokémon in middle school.

What's really cool about that emulator is the way its sound emulation works. Instead of emulating the Gameboy's synthesizer synchronously and outputting a PCM waveform to a buffer, which is probably impossible on J2ME due to hardware and platform constraints, it uses the phone's own MIDI (or square wave) synthesizer to play whatever the GameBoy synthesizer should be playing. This gives the video game music a very idiosyncratic sound when played back in MeBoy.

I used to run MeBoy under Sony w200 phone. With some frameskip Zelda for the GB was somehow playable. Pokémon ran well enough OFC.