You can only access the Sevii islands after you've been taken there by Bill. Otherwise, you can take a fast ship from Vermillion City, the same place you boarded the SS Anne.
When you defeat the gym on Cinnabar Island you will meet Bill outside. He will ferry you to Island One to meet Celio. Bill will then give you a Meteorite and the Tri-pass which will give you access to Island One, Two and Three.How_do_you_unlock_islands_after_beating_the_elite_four
Bill gives it to you after getting to one island.
Defeat Blaine. When you come outside his gym, Bill comes and tells you he got invited to One Island by his friend Celio and asks if you want to come with him and you get on a boat to One Island.
To get the Tri Pass, you must progress in the game until you get to the Cinnabar Gym. After you beat it, when you leave the gym, Bill appears and talks to you. Then he will give you a Tri Pass and sends you to One Island to talk to Celio.
MT. Ember is a Volcano in the One island. You will need a Tri-Pass to get into the One Island. You can get into the One Island and get the Tri-Pass by Defeating the 7th Gym Leader Blaine. Bill will take you in there, and Celio will give you the pass
do the errand for bill on one island.
Beat Blaine on Cinnabar Island and Bill will take you to One, Two, and Three Island.
You will need have beaten Blaine on Cinnabar Island to gain access to Island One. When you exit the Gym, Bill will ask a favour and take you to Island One.
he will be in the Pokemon center in cinnabar island you can just talk to him.
Go into the Pokemon center on Cinnabar island and talk to bill (he's over on the right).
When you defeat the gym on Cinnabar Island you will meet Bill outside. He will ferry you to Island One to meet Celio. Bill will then give you a Meteorite and the Tri-pass which will give you access to Island One, Two and Three.How_do_you_unlock_islands_after_beating_the_elite_four
on one island after you defeated the 7th gym bill will come to you and he askes if you want to come to one island
Get the 7th badge from cinnibar island then you will see Bill outside of the gym say YES to his question to be transported to one island!
Bill gives it to you after getting to one island.
Bill and his friend will pick you up on cinabar island, once you defeat Blaine.
Bill asks you to go to one island not four island and second of all if you finish the 1-3 island sidequest and get the ruby and deliver it to Celio you can go to islands 4-7.
You go to one,two,and three island with Bill.