A Kickstarter project was successfully funded to manufacture an adapter for the iPhone that will fit 1-1.5" eyepieces for telescopes (among other devices). It sells for $80 starting June 30.



It's an afocal, no-lens design. The iPhone 4S has a back-illuminated, f/2.4 CMOS camera [2].
Links:
[1] http://www.kickstarter.com/projects/637232010/magnifi-the-worlds-first-iphone-photoadapter-case
[2] http://parasam.me/2012/03/11/iphone4s-section-3-specifications-hardware/
[3] http://www.aavso.org/forums/variable-star-observing/photometry