If you don't feel like permanently altering your phone with a macro lens, hacker Thomas shows us how to make a detachable one using a lens from mini binoculars.
You can really use any lens that has a circular casing around it, as the idea is that it will go in front of your phone's current lens as a separate attachment. Thomas essentially took a lens from a pair of mini binoculars, made a mounting bracket with some epoxy putty, and put a headphone jack on top to attach it (it doesn't actually use the headphone jack for anything except stabilisation). It's a pretty clever workaround for those that don't feel like opening up their phone, and pretty easy to do. Hit the link for more instructions and photos.