Perhaps Jon's subconscious mind was merely giving him the encouragement and comfort his grandmother symbolizes at a time when he needed it, but who's to say we can't connect with the other side through our dreams?  Think about it, everything that exists gives off a vibration and travels in waves... radio, sound, light, etc.  Our brains give off waves too and when we go to sleep and enter the REM state (the dreaming state) our brain waves slow down.  Perhaps that is just the right frequency needed to "tune in" to the other side!