// Use it like so

if ($shortlink=get_short_link("http://www.cnn.com/")) 
	echo $shortlink;
} else {
	die("There's been a grave error");
}

// And here's the function

function get_short_link($url) {
// http://james.cridland.net/code
// v0.2 24 May 08: added a URLdecode function, to correctly cope with some charactersets
//                 thanks to Nick at www.japansoc.com

$bitly_login="yourloginname";
$bitly_apikey="yourapikey";

$api_call = file_get_contents("http://api.bit.ly/shorten?version=2.0.1&longUrl=".$url."&login=".$bitly_login."&apiKey=".$bitly_apikey);

$bitlyinfo=json_decode(utf8_encode($api_call),true);

if ($bitlyinfo['errorCode']==0) {
return $bitlyinfo['results'][urldecode($url)]['shortUrl'];
} else {
return false;
}

}