From Bulbapedia, the community-driven Pokémon encyclopedia.
Professor Oak's Pokémon Talk is a radio show. It is hosted by Professor Oak and DJ Mary, and is prerecorded. The show operates on the radio frequency 4.5 in afternoons; during the morning, the Pokédex Show is broadcast.
The show was initially started sometime after the events of Pokémon FireRed and LeafGreen. One of Professor Oak's aides claimed that it was going to be called "Prof. Oak's Pokémon Seminar".