Sorry I lost your number... (opens in new tab)

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.

I'm not sure how it works on Android but contact info gets synced on iPhone as well. The problem in the pitch is non-existant because when you upgrade to a new iPhone, you can restore contact data. Alternatively, if you move off the iPhone, the address book keeps a copy on your computer as well.

This is very different than your response here, which is less about losing contact info, more about always having an up to date source. Personally, I can only speak for myself but I don't see this as big of a problem.

I do acknowledge I've seen people post losing contact info (for whatever reason) at least once or twice on my time on facebook but of course thats not representative of how big the space is. However I'm not sure if this problem is big enough of an issue (just my two cents).