The Japanese company Adplus (gizmon.com) went a step further than the Leica iPhone stickers and designed a real Leica screw mount inspired case for iPhone 4/4s (similar to this Leica i9 concept). The Gizmon iCA has an optical viewfinder, shutter button, conversion lens mount, tripod socket and strap holes:
The Gizmon iCA is available in three colors and can be purchased here for $65:
Gizmon also offers the following additional accessories:
