[Users] what is the in_network table for

We have 1 asterisk and 1openser installation, with 1/2 of our users registering to one and 1/2 to the other. What I wanted to do for in network calling is add a column to in_network table thats called ip. In that column I want to put the ip address of the asterisk machine that the calls for those in network users that are registered to it should go. Then somehow set up openser to do a (lookup) then failing that look up the number in this database, if its rewritehost the call to ip in the ip column, else forward to our pstn gateway. Has anyone done this before, how would one handle multiple openser installations with 1/2 of the end users registering to one and the other 1/2 registering to the other barring a shared userloc database? What was the in_network table made for? As always any help greatly appreciated. Thank you.