GBA Emulator for iOS and Android.

For android its quite simple, google play store has tons of them.
To get roms go to coolrom.com, search the rom and download, instantly.installs to the app.

Apple doesn't. If you have a jail broken ipod its easier than not having one but not needed.

First step, set your date back to 2012.
Second step, go to Coolrom.com
Third step, select Emulators.
Fourth Step, select any of them.
Fifth step, (for GBA) choose the old on if you do not have iOS 7, new for iOS 77 users.
Sixth step, download and install.
Note : to download roms you need to keep the date back.

Get roms go to Coolrom.com and search the game you want, there's hacks of games so those are fun. For pokemon I suggest Advanced Adventure, Crystaldust, or Florasky or Dark Rising.