While it isn't the first product turning a smartphone into a microscope, the Micro Phone Lens is surely among the simplest solutions around. The accessory is pretty much just a tiny lens that you stick onto your phone's camera, gaining extra magnification for taking a closer look at stuff like the tracks on a circuit board or the wings of a fly...
Source: http://www.phonearena.com/news/Simple-lens-attachment-turns-smartphone-into-microscope_id46697
Source: http://www.phonearena.com/news/Simple-lens-attachment-turns-smartphone-into-microscope_id46697