If the iPhone's zoom just isn't doing it for you, and you prefer a higher-quality optical zoom to lesser digital zoom apps, DIY website Instructables details how to make a contraption that'll help you achieve just the frame you're looking for.
While this particular how-to is built for an iPhone, the idea can be easily used (or adjusted) for any phone with a camera. For this project, you'll need a jar lid, a suction cup and some old camera lenses — generally, if you're a camera buff, you may have some scrapped cameras around that you can steal these from. If you want to add a light source, too, you'll need a few more electrical supplies. The project also requires a bit of drilling and soldering, but nothing seasoned DIY vets like yourselves can't handle. Hit the link for the step-by-step guide.
iPhone Magnifying Camera Mod [Instructables]