What kind of phone to you have? If you have an Android and you're using Gameboid you need to:
1) Download "Lunar IPS"
2) Download the link in the first post of this thread
3) Get a Pokemon Emerald Rom (Google it, I can't post rom links on forums, because it is illegal)
4) "Patch" the ips file that you downloaded from this thread to the Emerald Rom
5) Download a gba.bios file
6) Plug your phone into your Computer and on the phone when it asks Use as Disk drive or Charge Only hit "Disk Drive"
7) Your computer will ask you how you want to use the phone, hit the option that lets you view the phone folders
8) Make another folder there and call it "Roms"
9) Move your gba.bios files and roms into the Roms folder
10) Now either unplug your phone, or use as "Charge Only"
11) Play and enjoy
Hope I helped! :)