Instructions
Select a Pokemon from one of the following evolutionary sets: Venonat, Dewgong, Chinchou, Porygon, Mareep, Remoraid, Volbeat, Joltik or Genesect. This includes the named Pokemon and any Pokemon which evolves from it.
Use the Pokemon in battles until it gains enough Experience Points to level up to the position between Levels 29 and 40 where it automatically learns Signal Beam.
Take other Pokemon, which cannot learn Signal Beam by leveling up, to the Move Tutor house in the Frontier Access area on Route 40 to the west of Olivine City.
Talk to the bottom-right of the three men in the house and ask him to teach one of your Pokemon the move "Signal Beam." You will be shown which of your traveling Pokemon are capable of learning the move.
Go north into the Battle Frontier and fight in battles there until you have won 40 Battle Points.
Go back to the Move Tutor in Frontier Access and pay him the 40 Battle Points to teach Signal Beam to one of your Pokemon.