Photon2 AddCalbackTarget
To register for callbacks, PhotonNetwork.AddCallbackTarget(<Your Component implementing this interface>); To stop getting callbacks, PhotonNetwork.RemoveCallbackTarget(<Your Component implementing this interface>);
You can also simply override MonoBehaviourPunCallbacks which will provide you with Magic Callbacks ( like Unity would call Start(), Update() on a MonoBehaviour)
Jesús Angarita