xmpphp/examples/sendmessage_example.php

<?php

// activate full error reporting
//error_reporting(E_ALL & E_STRICT);

include 'XMPPHP/XMPP.php';

#Use XMPPHP_Log::LEVEL_VERBOSE to get more logging for error reports
#If this doesn't work, are you running 64-bit PHP with < 5.2.6?
$conn = new XMPPHP_XMPP('talk.google.com', 5222, 'username', 'password', 'xmpphp', 'gmail.com', $printlog=false, $loglevel=XMPPHP_Log::LEVEL_INFO);

try {
    $conn->connect();
    $conn->processUntil('session_start');
    $conn->presence();
    $conn->message('someguy@someserver.net', 'This is a test message!');
    $conn->disconnect();
} catch(XMPPHP_Exception $e) {
    die($e->getMessage());
}