Thanks for posting. In order to enable an FXS port, you must create a voice user. This is done in the "User Accounts" in the web GUI, just be sure to specify "Analog station" so that you are prompted for the specific FXS interface to match up to an available phone number for this site. This process is pretty straightforward in the CLI as well.
voice user 5551000
connect fxs 0/1
sip-identity 5551000 T01 register auth-name 5551000 password 1234
The last line is optional, but I added it in case a registration is required by the softswitch. Of course, you'll need to have an available phone number to use on this line and the SIP server may need some additional configuration for this to work properly.