In certain situations, most notably if you are routed through an IP switch, it is essential for the country code to be set in the CLID data for PRI trunks.
Here's the short version:
If you are using CLID and are in North America, do this:
>ld 15 CDB000
REQ: chg TYPE: net
CLID yes ... INTL 1
The long version....
Recently, unknown to me, our telephone carrier cut us over to an IP switch for one of our ISDN-PRI trunks. When this happened, our international calls over that route started terminating on a "can't complete call" recording. I bypassed this route for international calls and placed a call to repair.
At first their repair department claimed that no network changes had been made and the problem was on my end. I knew that no changes had been made on my end, and domestic long distance and local calls were working on that route just fine, so I figured it wasn't hardware. It seemed like it had to be a routing problem.
Weeks passed. I was forced to escalate the problem.
After a great deal of haggling, repair finally admitted that we had been cut over to a different, IP based switch. The ticket was passed to the routing department and they set up some call traps on the PRI. They came back with the revelation that the NOA (Nature of Address) value in the D channel data was set to "international". They told me it should be "national" and that I had to reprogram my PBX, and they closed the ticket. Well, this made no sense to me since (1) it WAS an international call and (2) I can't control the value of the NOA message. That's a function of the PBX's call setup software.
Weeks passed. Another round of escalation phone calls yielded me a new ticket and a different repair technician.
This time he told me that the CALLING number NOA was wrong, not the CALLED number NOA. I did some research on the Internet to learn more about what the NOA does. It is basically a numeric value that represents the type of call; local, national, international, etc. At that point, in spite of what they told me, I started to look at the problem from the point of view that the NOA value was correct, since I can't control it. Something else had to be wrong.
I started examining my CLID configuration and found that the INTL parameter (country code - 1 for North America) had no value. This had never been a problem in the past since Caller ID was really only used for the benefit of the local E911 service center. They know what country we are in, so the country code had never been an issue. It turns out that for an IP based switch, the CLID data sent over the D channel is actually used for call routing. The country code becomes essential when routing international calls. I set the INTL parameter to 1 using LD15 and the calls started routing correctly again.
This is a simple setting, done in LD 15, as described in the short version above.