The contacts API (http://developer.yahoo.com/social/rest_api...ontact_api.html) will require an OAuth authenticated session in order to connect to the user's contact information. This would also require the user to grant your application permission to use their contact information, which I believe is done in a browser. There may be a way of conducting an auto-login and authentication using the username and password but I haven't tried this yet, and as far as I know user login and validation details are stored through cookies, so you would need that browser step.
Jonathan LeBlanc Senior Software Engineer Yahoo! Developer Network Twitter: jcleblanc