Everybody is opening up their closets these days — freeing up their source codes, bare opening their APIs. Yahoo! have released their Address Book API, which will give 3rd party developers access to Yahoo! users’ contact lists without the need for those traditional and primitive method of page scraping.
The Yahoo! Address Book (AB) API is a JSON/XML interface for accessing and updating the Yahoo! Address Book using a web service. It can be used to look up addresses for auto-completion of emails, to add addresses for future shipping information, to obtain unique identifiers for network invites, or to sync with another address book.
With this new release, there is no policy in place for restricting how long developers can store and use the data they pull from the API. But, as with many of its developer initiatives, Yahoo reserves the right to stop what it deems bad behavior. The Yahoo! Address Book API is limited to 5,000 queries per IP per day.
Visit Yahoo! Address Book API for all the details — How to use it?, API details, Tool & Documentations etc,
Google have also released their Contact API few months ago.