It's probably a symptom of Ooma's termination partner for the call not accepting the codecs that Ooma's network is telling them it has available. If I'm right, it's usually an issue they'll have to work out on their network or with the partner or by using a different partner for those calls. The one exception would be if you have LOW bandwidth conditions on your Internet connection and you can improve that to broaden the selection of codecs that can be used for the call.
Formerly employed at another VoIP company.
My opinions are my own.
"Please try to do a factory reset, here are the procedures:
1. Unplug unit from power for 30 seconds
2. After 30 seconds connect power to Telo
3. When the red ooma logo starts flashing press STOP and TRASH at the same time (the logo should flash blue/red)
4. hold the keys until the ooma logo turns solid red
5. the box should then factory reset and reboot
The ooma Telo will then go back to factory default settings and reboot itself. It will then start fresh like if it was used for the first time."