Heh heh, I guess we have to consider every possibility, even when the OP doesn't mention a potential cause like that.
Of course, we could explain how to look at the phone port voltages, but my bet is on a bad phone, unless the OP plugged both OBis into a live phone jack and a call came in, sending ring voltage into it.
Years ago, I recall accidentally mixing up the phone and POTS line cords, plugging the POTS cord into the wrong jack on a 110, and no magic smoke escaped, and it worked afterward.
I've never wanted to intentionally ruin an OBi, so I haven't tested whether the typical ~48VDC on-hook voltage will damage the OBi 200 series' SLIC, or if the SLIC can survive it. I know there is some internal protection circuit in the path, but I have no idea what it can withstand.