I have acquired a single SPA504G to test with our 3CX system. Our 3CX system is offsite, I use Option 66 for provisioning. I reset the phone to factory defaults, and updated the firmware to 7.5.7s. Our 3CX is v12.0.41311.996 SP.6.2. I created a new extension and added the MAC and chose Cisco SPA-504G as the model. Then I connected the phone to our network. It receives a DHCP address from our server, but never reaches the 3CX server to register or provision. Nothing in the server logs to indicate if it ever made it there. I then followed the instructions from this article http://www.3cx.com/sip-phones/cisco-spa/ and updated the profile rule using the admin interface on the phone. Still not connecting. I will try to roll back the firmware on the phone this afternoon to see if that has any effect, but I was wondering if any of you might have insight into something else I might have missed.