How do you become a member of team rocket?

in firered you must first beat the elite four 900 times then go back to the viridian gym Giovanni will be there then talk to him and he will ask you to join team rocket say yes then he will tell you to rob the celadon dept.store then go back to Giovanni and youll be in in leafgreen its the same you cant for ruby sapphire or emerald but beware once you join team rocket youll never be able to go into celadon city you wont be able to go to any pokemarts or Pokemon centers and non team rocket members will be afraid of you and if all your Pokemon faint your game save file will be lost