If you have an iPhone 3G/S, download the Sephora to Go app and then click on "Mobile Offers" after you open the app. Show it to a Sephora employee and you'll get a free case for your iPhone 3G/S! Click here to find a location near you.
If there is no Sephora near you, you can still get your free case! Just make a purchase at Sephora.com and enter the code MOBILE3 for a 3G/S case or MOBILE4 for a 4G case.
Thanks, Deal Seeking Mom!