You can buy dedicated iPhone bike mounts if you're so inclined, but this nifty hack makes it simple to affix an iPhone in a secure case to the front of any bike at very low cost.
Picture: Anthony Caruana
It's courtesy of friend of Lifehacker (and sometime contributor) Anthony Caruana, who hit upon the solution of using cable ties with an existing iPhone case that came with a belt clip, which is what he's adapted into a bike mount with a few simple, cheap and easily replaceable cable ties.
Caruana does note that it wobbles slightly, and a Bluetooth headset is recommended for when you're riding.
DIY iPhone Cycling Mount [Run And Lift]