I'm using SPA3102 with Gizmo5 SIP VoIP service currently without any PSTN connectivity. Outgoing calls are very fine. However, incoming calls are very unreliable, like only occasionally the attached analog phone rings. It's not a total no-ringing-at-all. After the SPA is rebooted, the attached analog phone rings for the first incoming call all very fine. However, the next incoming calls do not ring the analog phone at all. Sometimes after a reboot, several incoming calls ring the phone fine, but thereafter, no rings at all. I'm not sure if it's the SIP provider or the ATA device, as when I check the ATA's info page while the incoming call is made, it shows no incoming call at all. However, other SIP phones (SW on PC and iPod Touch) rings very fine. Out of frustration, I even upgraded the firmware (it was 3.x.x before the upgrade) to the newest 5.1.10 and still the same problem. Tomorrow, I'll bring in my GrandStream ATA from my home and make sure it's not the network or the analog phone issue. In the meantime, please advise me what to do in this situation, like whether to request an RMA (or would it be worthwhile at all?).
Please try the following. On each device, please set NAT Keeplive Enable to YES. Reboot and try again.
This is likely related to the fact that routers close the UDP ports after some time of inactivity.