Well, I have HeartGold Version, but I reckon the two are pretty similar. So, no, I don't think any trainer has Meganium (as in to battle), most probably not (as in trade), but the exception is the rival Silver, if you chose Totodile as your starter Pokemon, then yeah, he would have Meganium. Does that answer your question?
No trainer has a phanpy in Pokemon soul silver.
the fourth trainer in the elite four have a murkrow
yes huey he is in the lighthouse
No, you can not buy any land on Pokemon Heartgold or Soulsilver.
Pokefan carter who is located in route 14.
Headbutt is no a HM in Pokemon soulsilver. However a man in Ilex Forest will teach it to any Pokemon that can learn it.
No, there are no underwater routes in Pokemon HeartGold or SoulSilver. The HM Dive is not available in Pokemon HeartGold or SoulSilver.
I'm going to but i don't know many people who do
You CAN NOT become a Gym Leader in Pokemon HeartGold and SoulSilver or ANY MAIN SERIES POKEMON GAME.
You can use any type of Poke Ball that you want to catch Spheal in Pokemon SoulSilver.
A trainer in Iron Island has one
ditto and almost any Pokemon/mew and almost any Pokemon