3D with iPhone & iPod touch?!
Step 1. You only need 12 business cards and a roll of invisible tape.
Step 2. Tape 4 business cards together to form an open cuboid as shown below:
Step 3. Create a second cuboid and tape them together to form binoculars:
Step 4. Now let's create what will constitute one half of the device holder: tape 2 business cards side by side, place your device on them, draw along its border with a pencil, and fold along the trace.
Step 5. Repeat step 4 to create the other half of the device holder!
Step 6. Place the 2 halves of the device holder at one extremity of the binoculars with enough space to slide the device as illustrated below:
Step 7. Tape the 2 halves of the device holder below and above the binoculars:
Step 8. Place your device in the space created by the 2 halves of the device holder and tape their backs together to hold the device tightly enough but not too much so the device can slide in and out without difficulty (beforehand make sure that there is NO adhesive part of the tape that rubs against the device display!!!):
9) Et voilà, you just made your own stereoscope!
Now you need some side-by-side 3D content in parallel-eyes configuration (as opposed to crossed-eyes configuration), for example from here for some beautiful 3D images from museums or from YouTube for some 3D movies.
For 3D images, import them in the Photo Album of your device, start a slideshow, slide your device in your stereoscope (see note 1), and enjoy the beautiful 3D effect (see note 2)!
Next: the commercially available solutions and how they compared to this DIY 3D viewer...
1. Best results will be obtained with an iPhone or iPod touch with a "Retina Display".
2. Because each person has a different accommodation distance, you may not perceive distinctly 3D. You can improve this by creating another set of cuboid binoculars that slides in and out of the main ones like the cylinders of a telescope.