Here is the breakdown:
It's codec issue. Codec is negotiated after the call is answered. And that is why call is getting disconnected.
You need to check the region setting
Check the Device Pool and Region of the GK Trunk
Check the Device Pool and Region of the Remore Phone
What codec is configured between them? Same thing needs to be done on the other cluster who is making call.
If you make the remote phone same device as the Local Phone on Cluster A, it should work.
I am still trying to gain access into the other Cluster A CUCM. I was thinking Codec negotiation also. I am set to use G.729 but blew it out to Swideband so it should negotiate any codec the other end is advertising but I still got a fast busy. I will update as soon as I get access.
Thaks for the input!