Ok, that was fun. Seriously, it was. But let's raise the stakes a bit. Let's lookup the caller, and try to greet known callers by name:
quickstart/twiml/1.1/hello-monkey.php<?php
// make an associative array of callers we know, indexed by phone number
$people = array(
"4158675309"=>"Curious George",
"4158675310"=>"Boots",
"4158675311"=>"Virgil",
"4158675312"=>"Marcel"
);
// if the caller is known, then greet them by name
// otherwise, consider them just another monkey
if(!$name = $people[$_REQUEST['Caller']])
$name = "Monkey";
// now greet the caller
header("content-type: text/xml");
echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
?>
<Response>
<Say>Hello <?php echo $name ?>.</Say>
</Response>
If you add your phone number and name to the $people array you can listen to Twilio greet you by name.