You will need:
Goomba - Click Here for download
Some Gameboy Roms
A Gameboy Emulator/gpSPhone
---------
1. Extract the Goomba emulator. Once you have done this run Goomba. First things first, Click the Grey Button next to the "Select Emulator File", then choose "Goomba.gba"
2. Click the Grey Button next to the "Select Output File" put in the name of the ROM you are converting. E.g. If you are converting 'Pokemon Blue', Name it "Pokemon Blue". Simple.
3. Now on to adding the '.gb' file that we will be converting to a '.gba' file. Where it says "Add GB/GBC Games" then browse to your '.gb' ROM. Once you have located the file, it will show up in the White Box below.
4. Click on the ROM, then choose 'Add ->'. Now all you need to do is click "Compile" it will then generate a new file with an extension of '.gba'. Congratulations.