load balancing over parallel links

I have 2 7200 routers connected over parallel e1 links.The first router is connected in Manila which connected to 6506 switch, in this switch the agents pc connected. The second 7200 router connected to 3750 switch at US side. My problem how can I implement load balancing on these devices. Main traffic is Voip since this a call center.6506 sw Ios 12.0,routers:12.2 and 12.1 IOS. Any idea on how to load balance and how to deploy QoS?