Hi, I have successfully make outbound call from X-Lite on my computer to Axon to Grandstream FXO Gateway to PSTN.
It is actually very simple.
1) create extension ID or using the default 101 - 110 and login to Axon with X-Lite or your IP-Phone
2) create external lines with a user id and password, then login to Axon with your FXO gateway. Once connected, you should see it say "registered" on your gateway.
3) create dailing plans and select the dail on line where your just created on step 2.
4) you should be able to make call to PSTN now.