To tell you the truth, I don't know as well. We had a customer who was forwarding their calls to an answering service at night. They had a full PRI setup. Then one weekend this just stopped working. I came in on a saturday and setup a work around to make it work. When I came in the following week I was still stuck on the situation. I finally called tech support and they said, turn that feature on. Once I did the forwarding was working just fine. So I honestly have no idea why it just randomly stops working.