This is an example how to configure two Call Manager which are in neighbor and call each other. (similar to existing PSTN international call).

If you want to use Call Manager to manage several gateways, and each gateway is in a different country not the same country with its local Call Manager.  Each gateway may terminate calls within its own country and also other countries.  The gateways send the destination number in E.164 format to local or remote Call Manager.

The dial rule for two neighbor Call Manager is as follows.

Exit Zone Prefix + Neighbor Gk Zone Prefix + destination E.164 number.
 
For example, 
GW-49 is in Germany and can terminate calls in Germany (country code 49) and Switzerland (41).
GW-1 is in USA and can terminate calls in USA and Canada (1), Mexico (52), and Italy (39).
GW-49 and GW-1 register in Call Manager A (CM-A).

GW-65 is in Singapore.
GW-65 registers in Call Manager B (CM-B).
 
These are the settings in Call Manager A and B:

CM-A setting:
Gatekeeper Zone = blank (No assign zone number in CM-A. CM-A accept any call from negihbor CM call)
Exit Zone Prefix = * (There is no exit zone prefix when call from CM-A to CM-B)
Neighbor Gk Zone Prefix = 0 ( CM-B zone prefix)
GW-49 Prefix = 49 and 41 (two prefix number in CM-A assign to GW-49)
GW-1 Prefix = 1, 52, and 39 (Three prefix number in CM-A assign to GW-1)
 
Setting of CM-B:
Gatekeeper Zone =  0 (Assign an zone prefix in CM-B)
Exit Zone Prefix = 9 (Prefix number when you dila from CM-B to CM-A)
Neighbor Gk Zone Prefix =  * (because call manager A do not check zone number) 
 
- When GW- 65  wants to call USA, it sends  91xx...x to Call Manager A from CM-B.  Call Manager A matches zone number 9 and prefix 1 in the prefixes of GW-1 and sends 1xx...x to GW-1. Note: There is no setting Gatekeeper Zone in CM-A. And Exit Zone Prefix is 9 at CM-B.
- When GW-49 wants to call Italy, it sends 39xx...x to Call Manager A.  Call Manager A matches 39 in the prefixes of GW-1 and sends 39xx...x to GW-1.
- When GW-49 wants to call USA, it sends 1xx...x to Call Manager A.  Call Manager A matches 1 in the prefixes of GW-1 and sends 1xx...x to GW-1.
- When GW-49 wants to call Singapore, it sends 065xx...x to Call Manager B from CM-A.  Call Manager A matches 0 in the neighbor gatekeeper Exit Zone Prefix and sends 65xx...x to CM-B. Note: There is no setting of Exit zone prefix at CM-A.

At this example, CM-A do not have a Gatekeeper zone setting. When GW-65 call to CM-A, an Exit zone prefix=9 in CM-B must start before your dialing number. Call Manager A accept all calls from neighbor and transfer to the destination number.