VOIP Problem

I know a lot of very intelligent people hang out here and was hoping someone could help. I am using Sunrocket VOIP which has an interface called a "Gizmo". They recommend putting the Gizmo between the modem and the(Linksys wireless)router. All is OK except when I play Halo online. If I happen to try to connect to a full server I get a message saying the server is full, which is normal, but then I lose my internet connection after the Gizmo for a couple minutes. The VOIP still works. This only happens with the Gizmo between the modem and router not if I connect the Gizmo after the router. Sunrocket tech support has been no help. Thanks