Not sure if anyone else have been looking for a cheap way to mount their iPhone to their bicycle, but I have found a way that works great for me. Using a broken OtterBox Defender belt holster and a couple of stainless steel cable ties from the hardware store, I was able to fashion a fairly stable mount for my iPhone. Basically I drilled four fairly centered holes into the belt holster and then threaded the stainless steel cable ties through and around my stem. Pics of the installation are here.