I recently wanted to find out if I was officially out of warranty coverage on my iPhone 3GS. I went into a local Apple store and was told to call 1-800-APL-CARE, or wait for one the Apple's "Genius" (or whatever they call them these days). I really didn't feel like waiting around for about 40 minutes.
I hated the idea of calling customer service, so I decided to figure it out myself. What I found out, is if you open iTunes, hold down CTRL+SHIFT key, and select Help > About iTunes, in the About dialog your phone's serial number will be displayed.

After you have the serial number go to the following web page.
I hated the idea of calling customer service, so I decided to figure it out myself. What I found out, is if you open iTunes, hold down CTRL+SHIFT key, and select Help > About iTunes, in the About dialog your phone's serial number will be displayed.
(Note: Press the CTRL, or SHIFT keys to control the up/down scrolling, press the Space Bar to pause or play the scrolling)

After you have the serial number go to the following web page.