I thought about this later in the day after I answered, and realized that you'd have to route based on the callers number (which probably won't do you much good), or, as if it was a DID. If the 800 number calls are coming in over the same trunk group as other calls, then you would have to have the ability (from your provider) to be able to identify the number that the person has called, in the same way you route a DID number. If your provider us unable to do this for you, then you will not be able to "pick out" only the calls made to the 800 number.