[Serusers] SRC-Based Routing?

I am using SER is the primary SIP server in front of four Asterisk PBX's each located in a different city(e.g., City 1: 899xxxx, City 2: 598xxxx, City 3: 356xxxx, City 4: 829xxxx). Users are identified by a 7 digit number based on their home city. For PSTN-bound destinations, I want to be able to direct SIP calls to the appropriate Asterisk server based on who is calling. Using the src IP address isn't sufficient as users move around the network - in one city one day and another city another day. For example, I want a call from user 8991234(a)domain.com to 91234567(a)domain.com to be sent to the server in City 1 because user 8991234 resides in City 1. I can't use the src ip address because users move around in the network. I have wondered about using a city-based db in addition to a global db. Being a newcomer to this, I'm hoping that there is a simple solution to this problem. Your help and insights would be greatly appreciated, Duncan --- <mailto:Duncan.Glendinning@cox.net> Duncan.Glendinning(a)cox.net