QoS over an ATM Network

I have an ATM network with a Nortel Meridian 1 switch. Access to the ATM network is through Sonoma Universal Edge devices (either 624 or the 612 here at the central office). I am attempting to get QoS up and running over this network. I am being told by my consultants that QoS will not run across the ATM network. They state if I plug the cisco routers (2621 at sites & 3700 here central office) into the Ethernet port on the Sonoma Universal Edge device that QoS will be removed. That going from IP – Ethernet – ATM will not allow QoS to route across the network. I do not have any experience with VoIP therefore do not know if they are fully up on the subject or wanting to sell me additional hardware. Can someone with VoIP and QoS experience give me some insight on this matter. I would particularly like to “hear” from someone with VoIP running over an ATM network. Thanks