After you migrate the phone system from analog PBX to IP PBX, if you have some analog phones, you can use the FXS gateway to make a connection between analog phones and IPPBX, at this time, FXS gateway needs to register to IPPBX as SIP extensions.
Here we take audiocodes FXS gateway and 3CX IPPBX for example, and we assume that they are in the same local network.
Firstly, we need to create the user in the 3CX:
After that, please login the web page of audiocodes FXS gateway, and put the user info into the gateway:
After we finish the settings of gateway, we can find the registration status here:
If it displays registered, you can use the analog phone of FXS port to call now.