[tatnai]

GrandCentral GC gives you an online phone number. You then register any phones you want to that number. When someone calls your GC number, it rings all/some of the phones you registered, depending on your setup. You can also call out with GC - this is what you are looking for. GC allows you to click to call from your website address book, and when you do this GC calls your phone, and after you pick up calls the number you are trying to dial. It can dial any number in north america. The GC dialer that you linked to is simply a front end for the click to call service on the website, making it more convenient. Many people use GC to get free incoming/outgoing calls by registering their GC number with their cell phone carrier for services like My Favs, Sprint-to-Home, etc that allows unlimited calling to a specific number (or a few numbers).