From the code, /join <channel> is a valid command, but the <channel> is not used.
The function looks like this in the current version:
function Cmd_join(&$xml_reponse, $clientid, $newchat)
{
$c =& phpFreeChatConfig::Instance();
}
So, $newchat is not being used. Just wondered if this is something known and "coming later", or if it's a bug.