I just do not see this working out. What I'd rather use is something like Gravatar for my address book details. People could register their address book details with email addresses, Twitter and Facebook and others could request more details through an API which enforces a privacy policy. I'd manage a whitelist of my contacts who are allowed to access my current address book details with specific access for groups. Like co-workers/colleagues could get my work email, work phone # but not my home address and home #. Having to use yet another app is very unappealing. With an API many of the apps I am using already can use the API, just like Gravatar is used by many apps. This is the way I'd solve this problem.