Doesn't look like you ever got an answer so, here's the solution:
Assume the following:
Main office - Axon 1
Remote office - Axon 2
Setup external line in Axon 1 (e.g.)
Line Name: remote01
ID or User Name: remote01
Password: remote01
-setup the external line to ring on an extension or group # as normal
Enable Use Gateway Server
Server: [enter fixed IP address of Remote office - Axon 2]:5060
Setup extension in Axon 2 (e.g.)
Extension ID: remote01
Display Name: remote01
Password: remote01
configure dialing plan, i.e. default
Once you've set these up you'll see the status in Axon 2's 'remote01' extension update to 'sip:remote01@[main office fixed ip address]:5060 with an expiry time.
Then do the opposite to connect your remote office to the main office, that is:
at the remote office, setup an external line, i.e. remote02
and at the main office, setup an extension to receive the login of the remote02 external line
Note: i would make sure you use two different userid's i.e. remote01 and remote02 because if you have an extension and an external line with the same userid, Axon may get confused if you want to use the extension or external line
Now if you've done it right, the external lines will be registered at each office's respective extensions and you should be able to call extensions between offices provided that your dialing plan is configured correctly to ring on the appropriate external lines, i.e. remote01 and remote02. You'll also be able dial local numbers, thus avoiding toll charges.
it's a bit of a pain, but that is the solution from NCH
p.s. make sure you open the below udp ports on the firewalls at each office and map/forward them to servers where Axon is installed, otherwise you may not hear any sound or have crappy quality.
UDP: 5060-5065, 5070-5080, and 8000-8020
p.s.s. get an adsl modem/firewall that has QOS too!