...
Assuming you have followed the quick start guide for the SPA3102, log into the web gui for the device (admin login / advanced ) and navigate to the Voice --> PSTN Line configuration and populate the Proxy / Registration and Subscriber Information ( make sure you set the Make Call / Ans Call Without Reg to yes) :
...
Determine "Line-In-Use Voltage" of the FXO port and adjust it to match
...