Hi,
Sorry about not saying nothing but I had other issues.
Regarding this, I managed to have one equipement that works for sure with dtmf and tested in that access, and the problem is the same!!!
This is for sure a problem with that gateway! We schedule an intervention with the operator in order to check everything. But by the way the client also has a bad opinion of this vine gateway... its also giving them internet access problems...
If this is really a problem of that gateway I apologize of having wasted your time...