Hi: I don't recall anyone ever mentioning any device like that, in all of the years I have been using VoIP hardware.
I think what you are describing is a box that has a microphone input jack, and a pair of phone jacks (or one phone jack and you use a splitter), right? Since it works with an analog (POTS) telephone, one would think it should work with the OBi devices, too, but the analog telephone specs are more forgiving as to audio power levels. I would think it would just sound crappy (over-driven or clipped audio) in that case, not that it would kill the OBi. That suggests that there is some way-out-of-spec signal (or harmonic distortion) being injected into the phone's audio path that is potentially damaging the telephone line interface circuit on the OBi.
If it were me, I would abandon that very old technology, and use something modern, like Skype, Google Hangouts or another audio/video service. They have the benefit of much better audio quality via wideband CODECs, vs. the very limited bandwidth of the POTS telephone standard. You could easily use any studio-quality mic and a headset.
