Reach Network is one of the best address book apps available on iOS(thenextweb.com)

http://thenextweb.com/apps/2013/05/02/reach-network-is-an-address-book-app-for-ios-that-updates-your-contacts-information-in-real-time/?utm_source=HackerNews&utm_medium=share%2Bbutton&utm_content=Reach%20Network%20is%20an%20address%20book%20app%20for%20iOS%20that%20updates%20your%20contacts%E2%80%99%20information%20in%20real-time&utm_campaign=social%2Bmedia