I use the DPH-50U to access voicemail and conference bridges all the time but the responder doesn't recognize the tones being sent from the phones through the DPH-50u. Sending the tones directly from the phone on a standard POTS works fine. When I send the DTMF tones directly from the Skype screen on my PC they also work. What can I do to make the DTMF tones pass properly through the system?