Matt, I read on one of this boards that is not necesary to have a gatekeeper to talk from one ATA to another. If all what you want is call from one office to the other “point to point” you could call from one ATA to the other by “dialing ” the I.P. address of the other device.Is something like pick-up the phone and dial * plus the I.P. of the remote unit and close with #. If it is your internal network you may pick up a easy I.P. number to remember.
On brands and features, I has been using Quintum for about a month now and VERY HAPPY with it. I have a two ports unit at my home,a four ports at my office across town and a two ports in South America where my family is. All that for less than $2k.
If you need help, give a e-mail at email@example.com
Good luck down under!