It is quite tricky holding the microscope in just the right place - in line with the camera lens of the iPhone.
When I first tried it with the standard phone app all I got was a small circle in the centre of the screen but using the app Camera+ which allows better magnification the view could be made larger.
Not the most brilliant of pictures but the following two shots are of what I assume to be a weevil of some sort (possibly a biscuit beetle) which arrived in a bag of broken dog biscuits. As can be seen from the photo above they are small, about 4mm long so as a cheap microscope the setup does a reasonable job.
The photos are unedited - exactly as taken by the phone.
The idea came from something I saw on the net. In that description the author had cemented the microscope to a clear plastic clip on shell for the iPhone. I was sure the article was on the Instructables site but I can't find it at the moment. There are lots of other ideas on there to achieve similar results.
I was wrong. You can see the original idea on the Crabfu blog HERE where there is a YouTube video.