It's very simple,
1) Log into your Axon web control panel
2) Click 'External Lines'
3) Click 'Add New External Line'
4) Set 'Line Name' to anything of your choice (just for your reference)
5) Set 'ID or Username' to your Teliax username, and password to your Teliax password
6) Then choose the extension or ring group incoming calls should go to
7) Select 'Use Gateway Server' and enter voip.teliax.com into the textbox
8) Save changes and you should be good to go
Note: Incoming calls should start to work right away, outgoing calls require you to setup a dialing plan (like Asterisk)
To setup a dialing plan,
1) Click 'Dialing Plans' in the Axon web control panel
2) Click the Edit icon on the default dialing plan
3) At the bottom of the page, set 'If none of the above applies, dial on line' to your Teliax line. If you want a more advanced dial plan you can come back later and add additional dialing rules (so for example you can call internal extensions.. the way it would be setup now is all calls our routed through to Teliax).