You need to activate the Network Machine on One Island. After you beat the Elite Four, go to One Island and Celio will ask you to get a Ruby from Mt. Ember. Once there, you'll find that Team Rocket was already there. Once you deal with them, you'll find an item called a "Ruby". Bring this back to Celio and he'll replace your tri-pass with a Rainbow pass which will allow you to travel to the remaining 4 islands of the Sevii Islands. Go to the 4th island and you'll find Team Rocket harrassing the local Ice Pokemon. You'll then "team up" with Lorelei and ruin their scheme (step may not be necessary). Now you go to the sixth island. From here head south until you are at a door with dots on it. Use Cut on the door and it will open. I forget the order, but then there will be a sign with dots on it surrounded by 4 holes north, south, east, and west of it. If the sign has 2 characters, go UP, 4 either go LEFT or DOWN, 5 go RIGHT. It pretty much corresponds with the amount of letters in the direction. Now you will find the "Sapphire" item. However, Team Rocket steals the sapphire from you and you have to track them down at their Rocket warehouse on the fifth island. Beat them, and you'll get the sapphire back. Bring this item back to Celio and he'll establish a connection to Hoenn. You can now trade with Ruby, Sapphire and Emerald. Does this help or should I elaborate more?