We had power outages here in CA last week. Since then I was having very frustrating problems calling out and getting nothing - no ring tone. Come to find out Ooma was calling the number and it was ringing other person/org. but I could hear neither. So they would pick up phone and hear but I couldn't hear them (not sure if they heard me).
I went into my Ooma Setup settings >MODEM Port MAC Address > and changed from "Automatic:" to; "Use Built in:" due to a prior post on the subject of not being able to call out. after doing that, on calling out I got busy signal on any number I called. I then changed back to Automatic and the problem seemed to have resolved itself.
Odd, but it seems to have worked. Hope this helps someone.