iMore has an article indicating that theft of iPhones has drastically declined thanks to the activation lock feature that was introduced in iOS. Activation Lock is a feature of “Find My iPhone” that requires that your iTunes username and password be used when trying to erase a device or reactivating a device. Apple prompts you to enable “Find My iPhone” during the initial setup. After being enabled, a device cannot be erased or re-activated without the iTunes username and password being entered.
This feature works on any device that iOS 7 can be installed on. That includes all models of the iPhone and iPad currently being sold. To determine if you have this feature enabled, check settings, iCloud, and make sure Find My iPad is enabled. For more information see Apple’s support page.