TO GET TO THE OTHER ISLANDS, YOU NEED TO BEAT THE ELITE 4, THEN GO TO THE NETWORK CENTER ON 1 ISLAND AND TALK TO CELIO. HE WILL SAY SOMETHING ABOUT YOU RUNNING AN ERRAND FOR YOU. HE WILL GIVE YOU THE RAINBOW PASS, WHICH ALLOWS YOU TO ACCESS THE OTHER ISLANDS. TO GET THE SAPHIRE, GO TO 5 ISLAND (I THINK) AND BATTLE SOME GUY STANDING IN FRONT OF A BIG METAL THING. AFTER BEATING HIM, USE CUT ON THE DOOR, AND IT WILL OPEN. MANUVER YOUR WAY TO THE BOTTOM (THE BRAIL IN THE CENTER TELLS YOU WHICH HOLE TO DROP INTO) AND PICK UP THE SAPHIRE.A TEAM ROCKET GUY STEALS IT AND YOU HAVE TO GET TO THEIR HIDEOUT ON ONE OF THE ISLANDS TO GET IT BACK OFF OF THEM. AS FOR THE RUBY, GO TO MT. EMBER, WHERE THE TWO ROCKET GOONS WERE, AND THERE IS A HOLE BEHIND THEM. BATTLE THEM, THEN WHEN YOU BEAT THEM, GO THROUGH THE CAVE. (I THINK IT IS JUST LIKE THE SAPHIRE CAVE)RETURN THEM TO CELIO, AND HE WILL PUT THEM IN THE MACHINE. NOW YOU CAN TRADE WITH ALL THE OTHER GBA POKEMON GAMES!
HOPE I HELPED!