A call center that buys

I’ve been reading a lot about call centers that sell products or provide services. The main idea in this kind of call center is to attend as much clients as possible in the better way is possible. But my trouble is a little bit different. I have a call center where we buy service (freights from drivers that call us). In this case, it’s not interesting for us to attend all the calls. Frequently, we have much more available drivers than deliveries to be done. The drivers doesn’t pay for the calls, so, one driver calls 5 or 6 times by day looking for a delivery, and we have to pay for each call. Does anyone know some similar case?