If you have a dedicated server which is *not* a bf2 ranked server, you can set up the dedicated voip server there.

Simply install the bf2 dedicated server, the voip server is included.
You will then edit voip.con with a list of ports and the “shared
password” to connect. Example:

55030 somepasshere

55031 anotherpassthere

Then make sure *all* voip ports on your servers are unique.

A single VOIP server can host up to 30 ports, you will then need to
create multiple instances if you need more.  Please note however,
that this functionality only works correctly on Windows servers. 
Also your individual BF2 instances you want to use your standalone VOIP
server should be configured with the VOIP server’s ip and port.