I've had this issue since I started with the service for about a year. It's pretty annoying. I use my voipo line to call into conference calls when I'm at home sometimes. I have to use my other VoIP provider sometimes because voipo isn't transmitting the DTMF correctly.

They have been pretty helpful in trying to resolve it, but they haven't had any luck. I guess its just a limitation of the VoIPo service or the carriers they contract with?

It's been kind of annoying and one of those things I will think about when I decide whether to keep going with VoIPo