There are a couple of PHP-related mailing lists available. The main list for PHP3 is: php3@lists.php.net. You may subscribe to this list by sending a blank message to php3-subscribe@lists.php.net. An archive for this list can be found at: http://www.tryc.on.ca/php3.html.

If you are interested in helping out with the development of PHP3 you should join the developers' list by sending an empty message to php-dev-subscribe@php.iquest.net.