This is a two line phone with an OBI-200 connected to line 2. I get no notification of inbound calls on the line 2 (no ring, "Line 2" light does not illuminate) but the call definitely coming through and I can blindly answer inbound calls and it works fine. So I believe the problem is in the ringer settings (or something equivalent) for the OBI device. Reasonable search efforts led me to trying increasing the ring voltage to 82volts (I also tried 90 volts just for funsies) and change the ringer waveform to trapezoidal. No effect.
Any other thoughts? Everything else seems to work fine - good dial tone, calls connect, everything except I'm blind to incoming calls.