These DIY lenses and filters are all inexpensive and add a bit of fun to your phone photography. But if you're looking to spend some serious cash on phone lenses, take a look at the Zeiss ExoLens for iPhone or the Olloclip for iPhone or Android handsets.
DIY macro lens
Grab a jeweller's loupe or stand magnifier for this one, as well as some mounting putty.
Make a long strip of putty that will fit around the eyepiece of the loupe and position it over the lens.
Open the camera app to properly position the loupe to ensure it's not causing vignetting.
For best results, hold the loupe close or on top of the subject you are photographing. Adjust focus as necessary using the camera app.
See some more examples of photos taken with this lens (and all the others) in the video above.
For this DIY use an LED camping light (often called UFO light) which you can find on sites like Amazon. Grab some velcro with adhesive backing and position it on the phone case so the lens looks through the center hole of the light. The velcro helps you to reposition the light as you need and also means you can remove it easier than double-sided tape.
As the ring light provides even illumination that helps to eliminate shadows, it's useful for portraits and macro photography. Thanks to Simon Ellingworth for the inspiration on this one.
You will need a soft jelly case, paper fastener and colored gels or thick cellophane. Cut squares of the colored gels that will fit over the lens with enough room to fasten to the case. Mark a spot for the pin to push through both the gels and the case, then cut a small hole with a safety knife.
Attach the pin and firmly fasten at the back to keep everything together, with enough give to let the gels rotate in front of the lens freely when you pull them back and forth. Use a small piece of tape to fasten the pins to the inside of the case just so you don't scratch your phone.
Try experimenting with different color combinations or just positioning the gel in front of the camera's LED flash (rather than the lens) for a different effect.
Try using a prism for creative effects. This will refract and distort light to create reflections, flares and unexpected results. Look for an equilateral glass or plastic prism like this one.
For more specific techniques on how to use a prism for photography, check out this article.
You can also use sunglasses as a filter. Depending on the lens, it will give your images a different tint. Try using sunglasses at sunset or on very bright days to alter the properties of the light entering the lens. If you have polarized sunglasses, try holding and rotating them in front of the phone lens to achieve a similar effect to using a polarizing filter.