Post a tweet to a user with the Twitter API

Question

I am using the Twitter Oauth API to post tweets on my Twitter timeline from my php application. It works well.

<?php $tweet = new TwitterOAuth($consumerKey, $consumerSecret, $OAuthToken, $OAuthSecret); $message = "This is a test message."; $tweet->post('statuses/update', array('status' => "$message")); ?> 

But I would like to know if there is an API that can post tweets on the timeline of my friends (the ones that I read on twitter)? Or twitter API allows you to post tweets only on the timeline of the authenticated user?