You have to go to a Pokemon event for the gba games (which they don't do since DS Pokemon came out) with a wireless adapter on your Gameboy SP or advance.
Find the Ruby inside Mt ember and then give it to Celio.
With the Rainbow Pass.
The rainbow pass is a key item in Pokemon FireRed version. To trigger the events to get it, you first need to own 60 different Pokemon.
on island 1, in the pokecenter. u can get to island 1 by acheiving the rainbow pass
Yes, Celio from One Island will give you the Rainbow Pass after you bring him the Ruby you find in Mount Ember. Of course, you can not get there unless you have beaten the Elite 4.
beat the elite 4
You need the Rainbow Pass
You can't because the Rainbow Pass is a Key Item which can't be traded without a hack or glitch.
First, beat the elite four. Then get at least 60 on your pokedex. Talk to oak, and he will give it to you.
you have to find the ruby in mt ember and bring it to celio but first you need the national pokedex--Check this answer out: http://wiki.answers.com/Q/How_do_you_unlock_islands_after_beating_the_elite_four
It is not possible to obtain the rainbow pass in Pokémon Emerald. It is only available in Pokémon FireRed and LeafGreen.
Go to Vermilion and hop on the fairy. note: you need the tri pass or the rainbow pass.