Not just the backup.Maybe you can strech it by allowing a user to upload her address book to the site. Then the site automatically links everyone on your phone

Not just the backup.Maybe you can strech it by allowing a user to upload her address book to the site. Then the site automatically links everyone on your phone book to each others profiles and if anyone changes a phone number it has a cascading effect on everyone who is linked with them - this way phones numbers stay current easily. Also, you could offer functionality to send business cards to each other.And maybe even backup text messages. A social network for phones.