iPhone 4: small,thin,light,is also a computer, internet browser,photo and video playback system,MP3 player,text messager, telephone, AND has a 5 megapixel, backside-illuminated imaging sensor inside behind a 29mm-equivalent semi-wide angle lens in still mode, with an f/2.8 lens, shutter speeds from 1/15 second to a little over 1/10,000 second, ISO range 80 to 1,000.
Canon 5D: Full-frame sensor, good image quality, takes Canon and NIkon lenses with adapters (I have 13 Nikon lens adapters to Canon EF mount), good color, easy to work with image files. So-so light metering and exposure control system, kind of a slug in terms of response time, but it's payed for itself.
Nikon D2x: professional control system, astoundingly good wide-area "focus anywhere" AF system, 4-user-configureable settings banks, extremely long battery life, ultra-quick response in all areas, programmable FUNC button allows one-press and one-click switching of critical functions, shoots both 1.5x FOV and 2.0 FOV with one button-press, fabulous light metering and exposure system.