I have a few CIX1200 systems. I have any IP phone that has two issues that I can't resolved.
1. When the attendent transfers a call to me and I pick it up right away, I am unable to hear anyone and they can't hear me.
2. When I call someone and they place me on hold and I don't hear music on hold, the call is dropped and I have to call them back.
My phone is the only IP phone on the system. Am I missing something?

Check Program 250, FB 16 IPT NAT/no peer to peer

It shows enable. Should I change to disable?

yes and test

Actually, I think it needs to be enabled for remote IP phone

If that doesn't work try resetting the IPU card, just change the IP address hit submit , then re enter the original IP address