I do not see how you will be able to do it. A 1800 call and a local call to the same number looks the same when you have a incoming.
If you could see the ANI number and , you could ask your provider not to allow local calls to your 1800.
At that point, any call arriving at your quintum that hava a I.D. that is not local (diferent area code than yours) you could asume that is a 1800 call.
Good luck!!! By the way ,could you post what route do you have on Quintum???? Thanks!!!