[PHP] JSON in PHP5?

[Dan Zilavy]

I thought that the json extensions where in >=PHP5.2.  Here's my example file 
and the output.  What's up?  Do I need to install something else.

file:
<?php
echo "PHP version: ", phpversion(), "<br/>";
if (function_exists('json_encode'))
    echo "json_encode() exists";
else
    echo "json_encode() doesn't exist";
?>

output:
PHP version: 5.2.5
json_encode() doesn't exist