I'm concerned that packet serialization is causing my problems with VoIP call quality across my WAN circuit. In a multi-link situation, serialization issues can be resolved with interleaving of packets, but in my case I have on a single ethernet handoff for my WAN connection. Is my only option in this case to reduce MTU size?
Before getting the card, try the shaping configuration. In times of congestion, you should see packets dropped from the default class in the output of the command.