A first ferromagnetic piece of metal is attached to the inside surface of a stringed musical instrument such as an acoustic guitar, allowing an external magnetic mount to be attached to the musical instrument through the magnetic force of the magnetic mounts magnet on the first ferromagnetic piece of metal. One or more electronic device equipped with one or more ferromagnetic elements trapped, sandwiched, mounted on or made part of the device and/or a device protective case may then be softly, removably and firmly mounted to the outer surface of the instrument without chemically adhering to or disturbing the outer surface of the instrument through magnetic attachment to the magnetic mount. The inner-mounted ferromagnetic element may be attached permanently or removably to the inner surface of the instrument, so that the external magnetic mount may have its position adjusted for optimizing the position of the externally mounted device.