I have what appears to be a SPA3102 firmware bug. The problem can be duplicated and is repeatable. I am running SPA3102 firmware 5.1.10(GW).
After you receive an unanswered pstn call with ring-thru to the phone attached to the SPA3102, on future outgoing line 1 calls when you place an outgoing call, the outgoing call only offers the G711u codec. It does not offer the G729 codec. The problem is not corrected until you reboot the adapter (do a power cycle). If you have a voip provider that requires G729 you cannot place an outgoing line 1 call. Voip.ms is my provider that requires G729 and when you try to place the call with them, they return "sip 488 Not Acceptable here" error after you have received an unanswered incoming pstn line (FXO port) call.
A Wireshark trace shows the difference in the outgoing sip invite before (successful) and after (failed) the incoming pstn line call.