I just made an inexpensive microscope using my iPhone 4s and about 20 bucks worth of supplies. It took me about an hour to assemble, outside of the trip to a hardware store to get everything (though if I was better at construction I may have been done in only 20 or 30 minutes). I followed this tutorial to the tee, making sure to follow the link in the Youtube description for an exact list of what I would need. Here is the finished product, with my first microscopic photographs below. Please click on the images for hi-res. Thanks to kmyoshino!