Additionally, where on the PokéGear Radio should I click to activate the specific Sound?
Serebii says that you have to turn the Radio to the Pokémon March Channel. On Wednesdays, the “Hoenn Sound” show will play Hoenn Pokémon will appear, and on Thursdays, the “Sinnoh Sound” show will play and Sinnoh Pokémon will appear. This only happens after obtaining the National Pokedex, which is obtained by trying to board the S.S. Aqua after becoming Champion.
Hope I helped!