I have a customer with 3 sites that are networked via IP, specifically the Internet. They sling packets via their public IPs. 2 of the 3 can talk back and forth, transfer calls to each other with no problem. The 3rd site can make and receive calls from the other sites, but if this site receives a call from the outside, then tries to transfer it to one of the other networked sites they get the busy tone, and it doesnt work. I went through the Special Applications guide, but it looks like once you have a valid IP network, transferring calls to one another is a given, the switches are Officeserv 7100's any ideas?