said by fbruno:
Given a specific 1-800 number, how does Sip Broker subsequently handle the call and why are they willing to handle it for free?
They would use a termination carrier, the same as any other outbound VoIP call is handled.
Any carrier connecting a call to a 1-800 type of number receives a payment for carrying the call.
As you know, the [called] party pays a fee to receive that call, and some of that money goes to the carrier connecting the call. At very high volume, some money can be made.
This is why (for example) Alcazar Networks will gladly handle any TF calls that you choose to make. They get something out of it, and have a big enough volume to make it profitable. In fact, if you make a huge amount of TF calls they will even give a little money to you!
In SipBroker's case, they presumably are using one or more TF termination carriers, and getting some money back to help support the rest of their operation.