How do you obtain the poke flute in Soul Silver?

Answer 1

The PokéFlute isn't a key item, it's part of the Pokégear Radio Card's Radio Stations and in order to obtain it, you have to talk to the Manager in the Kanto Power Plant and then head inside the Cerulean Gym and then a Team Rocket Grunt will rush out. Head North to the Nugget Bridge and battle him. Head back inside the Cerulean City and go to the top-left area of the pool. You'll see 2 sets of life rings there, interact with the set on the right and you'll receive the Machine Part which you'll take back to the Power Plant Manager, as thanks he'll give you his Charge Beam TM. Head to the Radio Tower in Lavender Town and go inside there and talk to the guy in brown who is by the back wall, he'll upgrade your Radio Card so that you can listen to Kanto Radio Stations. Once you've obtained the Kanto Radio Expansion you'll have access to the PokéFlute Radio Station. Just head into the Pokégear, select the Radio button and manually move the cursor to the upper area of the touch screen radio and exit.