The Google Contacts Data API allows client applications to view and update Contacts content in the form of Google Data API feeds. Your client application can request a list of a user's contacts, edit or delete content in an existing contact, and query the content in an existing contact.
Additional contacts-related API's:

Plaxo Address Book Access Widget

Apex (Salesforce.com) API

Wakoopa API

Provider: Google Code	Submitted By: APIFinder.com Staff
License: Open (free)	Email: Email this contributor
Price: 0	Connection Protocols: Atom,Other
Notes: An account with Google Code is required to use this API.
Functions: Personal Information Management
Languages/OS: Web Service, Java, Other Language, PHP