adamj: We have 6 PC on the network (Not counting the server) and I had bad breakup on both G729a and Ulaw today with all the PC's off. ISP is Woosh so that could be the problem...
That pretty much explains your problem. VoIP over Woosh is terrible and QoS isn't going to help you when your ISP has their QoS set to prioritise their own VoIP service.