Just wanted to add my own 2 bits... I have a fairly basic config right now, ISA running all ports open. All my stations are Windows XP with Windows Messenger 4.6 build 073. Using the Firewall client on all machines. I understand all the SIP and UPnP challenges for Windows Messenger. However I do voice no problem to my brother who is not using a Firewall and using windows XP and same version of messenger. The catch is that he has to initiate voice conversations me, vise vera of course does not work. Does anyone know if Microsoft is planning UPnP support? Also I did try the Linksys NAT router that says right on the box UPnP support, dont buy it it, it does not work right and definately no Voice with MSN. I called their support and I had to get it out of them that their box is not working right. I still like ISA as the better firewall and especially for NAT.