One of my customers is using the Packet8 Virtual Office, and when my > computer calls him to deliver the messages, he cannot navigate via > DTMF. I hooked up a line analyzer and listened to the call, and all > I'm hearing on my end is a "blip blip blip" as he repeatedly presses > the key to save the message. The DTMF tone basically sounds like it > was clipped at just a few milliseconds ... in fact, I really cannot > discern if it's still a dual frequency tone or not.
I have no knowledge of Packet8 so this is just a wild guess. Based on your description, it sounds like the DTMF pad (phone) in use is polarity sensitive and the battery to the phone is reversed on an incoming call, thereby disabling the generation of DTMF tones. Simply replacing the phone might solve the problem. The "original" touch-tone phones were all polarity sensitive; AFAIK, none of the modern ones are.