I have some Zultys IP phones that I've got hooked up to a 3CX system for testing in preparation for purchasing a full license in the near future. I also have 3CXPhone installed on a PC. Each of them will eventually become "unregistered" on the server, and I have to reboot/restart to get them to register. Once they become unregistered, none of the other phones can reach them. Dialing that extension goes straight to VM. Any ideas?