ill try to put this a plan as possible
as long as with in your rooter you can set up Port Triggering and open 5060 udp and 5061 udp
no DMZ
no Port Forwarding apart from 80 with roots to my server for http
1 server then can handal 20 agents an then just get the other 20 agents to conect to the other server
then you can have 2 pbx's running (vicibox) as long as both are on difrent ip's (statick) then all should be fine....
or set up 3 vicibox 2 for the agents 1 for all calls point dmz to it and Port Forwarding
server for calls then conect to carrier and set up 2 softphones then with the setup info of the phones
add them as carrier info to the agents server's 1 phone for each server then agets servers can handel the agents withs the calling server maks all the calls
then when needed add more phones and add more servers
thir could be other ways of dowing it that are more complex but i like simples
an allways IPlock all server's DGG is a good start
ive got to admit it took me a week to figer it out but i maniged to set up a vicibox and a freepbx both using same carrier