In Pokémon Emerald:
1. Beat the Elite Four and get the National Dex
1. Beat the Elite Four
2. Have at least 60 Pokemon in your Pokedex
3. Talk to Prof. Oak after beating elite four and having 60+ Pokemon to receive the National dex and Rainbow Pass which allows you access to Islands 4-7
4. In One Island, talk to celio and agree to help him with his Network Machine
5. Obtain a Ruby and a Sapphire (not the games, they are actual items in the game) one is found inside Mt. Ember and the second is found in Six Island inside the cave
6. Bring the Ruby and the Sapphire to Celio and the Network Machine will work, allowing you compatibility with the Ruby/Sapphire/Emerald version.