Below is a list of the common problems with the SPA3102.
401 Unauthorized: The registration options within the SPA3102 admin PSTN tab need to be disabled.
503 Service Unavailable: Improperly wired phone line, phone line with no dial tone, or the Line-in-use voltage is higher than current from Info tab of the SPA3102 admin page.
These two simple problems are 90% of SPA3102 issues, double check the wiring and the line-in-use voltage and it should work.