How do you get to Pewter City in Pokemon SoulSilver?

Answer 1

After Getting 8 Badges and getting to Kanto via the S.S. Aqua, (and optionally a few Kanto badges), you are ready to get to Pewter City:

1. Get to Route 9 (East of Cerulean City) and Surf to get to Route 10.
2. Go into the Power Plant and talk to the manager
3. Go back to Cerulean City, enter the Gym
4. Chase the Team Rocket guy onto the bridge north of Cerulean and beat him
5. Find the machine part in the gym, and return it to the Power Plant
6. Go to the Lavender Town Radio Tower, and talk to the guy near the table by a window. He will give you the Radio Expansion card, so you can access more radio stations on your Pokégear.
7. Go back to Vermillion City, head east towards Snorlax. Find the Poké Flute Channel on your Pokégear and play it, then Snorlax will wake up and battle you.
8. After defeating or capturing Snorlax, go through the Digglet Cave, and use Cut on any of the trees on Route 2. Head north through Viridian Forest, and you have reached Pewter City. You can also go south to reach Viridian City and Pallet Town (and Cinnabar Island)