I have a customer with 3 sites with IP phones. The IP phones at the remote sites are connected to the main site thru a VPN tunnel. Is there any router port forwarding that needs to be programmed? The remote phones have poor call quality but the main site is crystal clear. We know that bandwidth may be part of the issue but are trying to eliminate anything else.

There is port forwarding required for registration & audio paths, but if the phones are working at all, this apparently has been done. You can do a little QoS programming to prioritize the phones to help with the poor bandwidth, but I would fix the bandwidth issue as quickly as possible to eliminate the problem.

If they are connected via VPN - that's all you need from the routers. No port forwarding needed. Keep in mind that VPNs are encrypted, and that requires extra bandwidth - as well as horsepower on the VPN routers. If the VPNs are carrying a lot of traffic besides the IP phones - then bandwidth is almost certainly the issue. What sort of quality problems are you having?