Pokémon HeartGold Version Unlockables

Play the old tunes from GSC
Did you know that you an unlock a Pokegear add-on that will allow you to play old tunes from Gold/Silver/Crystal versions?

GB Sound is located in the Key Items Pocket of your Bag. Once turned on it will replace the music and sounds with the music and sounds from the original games.
UnlockableHow to unlock
GB PlayerOnce you have collected all of the Kanto badges, go to the condominiums in Celadon City. Take the elevator to the third floor (it should say GameFreak Elevator once you enter). Speak to the person standing in front of the globe and he will give you an item called GB Sound.