[Craig B]

Like James has said, your after prioritising your VoIP and Video conferencing traffic. The buzz word your looking for is QoS (Quality of Service). Most routers can do this, although if your not sure about the technicalities then the Dryatek routers can configure QoS from a fairly simple web interface. Then you might pick VoIP and Video Conferencing to be high priority, email might be low priority (Most people don't mind if an email is delayed by a few seconds, but a voice call will be unusable with the same delay).