Edit: I originally said modem when I should have said router. My current modem+router is a combo. Anyway, I see that the power-cycling suggestion was the cure. Here is what I had meant to say, even though it is no longer relevant:
Try putting your
modem router model number into the search box above. Try the model with and without the hyphen if applicable.
Read
http://www.obitalk.com/forum/index.php?topic=33.0If QOS is on, turn it off for now.
If you are doing DMZ or port forwarding, turn it off for now.
If you changed any settings other than WiFi settings on your modem, change them back for now.
What happens if you dial **9 222 222 2222?
If you post about your problem again, identify your
modem router model, and maybe version. Identify changes you have made in the settings.
I have not experienced a problem getting VOIP through a
modem router. I did read other posts that suggest the above may be useful.