Recently I bought a macro lens for my iPhone from Photojojo and I must say its pretty awesome.
The lens is designed to attach to your phone with a magnet but seeing how the back of the iPhone is made out of glass it doesn't work so well. The lens ships with 2 metal ring with adhesive backs that are ment to be stuck to the phone to give the lens magnet something to attach to, but not only are these rings not very attractive, they would permanently cover your flash and over time slide and fall off the phone from having the phone in your pocket. What I needed was a removable metal surface for the lens to attach to that was simple to attach to the phone.
After kicking around a few ideas and looking around the house to see what materials I had available I came up with this small metal plate with an elastic tied to it.
I started with some generic metal strapping. It can be used for all kinds of jobs around the house.
The large holes in the metal strap happened to be the exact size of the camera lens on the iPhone 4 and the small holes are perfect for attach points for the elastic.
Using metal shears I cut off a piece consisting of 1 large hole with 2 small holes on each side. If you don't have metal shears you could use side cutters (wire cutters) but it will be a little more difficult.
After that you need to ensure all the edges are smooth so you don't scratch your phone or yourself. A metal file or sand paper will do the job. When your done you should have a blank that looks like this.
Now you need to make a few bends just past the small holes. One side need to bend up and the other down creating a "S" pattern. The point of these bends it to keep the metal flat against the phone when the elastics are tied to it. The reason for the bends it different directions is the downward bend will go over the top lip of the phone. You can do this easily using a pair of pliers.
Now for the elastic. I used a round fabric elastic because it's easier to tie knot but any type of elastic should work. First tie one end of the elastic to the metal plate and then holding the plate to over the camera lens with your thumb, stretch the elastic around the phone to determine where it needs to be tied on the other side. The elastic should be tight but not so tight it will be hard to put on.
And here's what it should look like when your done
Now whenever you want to attach your lens just slip on the metal plate and snap on the lens. If you only plan to use the lens this way you could use some epoxy and glue the lens to the metal plate to make it one piece, but I didn't try this as I plan to you the lens on my macbook also.
Did I mention I really like the macro lens :)