RingBack is a simple app that enables you to easily setup your lock screen with your name, a phone number to call and a reward (optional) in the event you lose your iPhone, iPad or iPod.
Otherwise, if you have locked the screen on your device the finder is unable to contact you. But, if you have not locked the screen your information (including your contacts, email and banking as well as other information) can be easily accessed. With Ringback it means your data is locked but the finder of your iPhone, iPad or iPod can still call you to return your device and claim the reward offered.