Instructions
Load your previously saved game of "Pokemon SoulSilver."
Play through the game until you reach the Radio Tower in Lavender Town. This tower used to be the Pokemon Tower in the previous games. Team Rocket's grunts have settled inside the tower.
Reach the top of the tower and fight the three Team Rocket bosses. These fights are not continuous, so you can return to the Pokemon Center in the northwest corner of the city after each fight if necessary. Defeating the bosses causes Team Rocket to leave the building.
Head to the bottom of the Radio Tower to find an old man waiting for you. Walk up to him and press "A." He will thank you for clearing out the tower and give you an expansion card, which is your key to the Pokeflute Channel.
Return to the Snorlax on Route 11. Press "X" and select your radio. Point to the top of the sphere until you hear the Pokeflute begin to play. Exit back into the game while it is playing to wake up Snorlax.