In the past few years, we have covered plenty of iPhone compatible microscopes here. The TinyScopeCAM is also worth a look. It is a 1000x iPhone microscope that you can take anywhere to closely observe insects, plants, and other samples. It has 3 illumination modes and focusing range of up to 0.25mm.
This iPhone microscope measures only 69.5mm x 56mm x 23mm. It is powered by a 5V power supply. This project is currently active on Kickstarter. You can back it here.