After looking around the MTBS3D Forums I stumbled across a design of a 3D printable mask to allow you to use your Android phone as a VR 3D HMD. (Original can be found here: http://www.durovis.com/index.html).
I liked the idea behind this but after printing the actual device there was a few bits that I didn't get on with so decided to start playing with Google sketchup to come up with my own version.
I printed this out on a RepRap so should print out fine on any 3d printer. You can then use the native Android Demos from the OpenDive website. Or you canuse the Vireio Perception drivers along with FreePIE and Splashtop to stream PC games to your phone in 3D with headtracking (This is not as good as a proper HMD such as the Oculus Rift but it does work!!)
This was designed to be used with my Samsung Galaxy S4 phone. But it should work with any Android Smartphone of a similar size.
This is fairly simple to build.
Print out the main body, The lens holder and 2 of the Head Clips.
You will need 2x 25mm Lenses (Something like the ones you get out of toy binoculars). I actually got mine out of a telescope eyepiece. You can also purchase a pair of lenses from the opendive website. You may need to sand the lens holes down slightly to get a tight fit for your lenses.
I have included the google sketchup files so if you need to modify the size of the holes for the lenses you can. You can also change the IPD to match your own so 3D viewing will be better.
Once you have printed the part, just put them all together and use 2 elastic bands to hold your phone.
Use 2 M3x20mm nuts and bolts to hold the lens holder in place once you have adjusted the focus to match your lenses. Then attach and elastic fabric band to use as a head strap.
I also used some 13mm Draft excluder to pad out the edges of the item so it doesn't damage your phone or your face!! :-)