Php-grandcentral-dialer is a project mainly written in PHP, it's free.
A simple PHP script that lets you dial a phone number using your Grand Central account.
Dialing a number is simple
$gc = new GrandCentral('<username>', '<password>');
$gc->call($your_phone_number, $their_phone_number);You can also use the included AppleScript file to dial a number directly from Address Book.
This code is released under the MIT Open Source License. Feel free to do whatever you want with it.