DTMF Tones

VoIP - Incoming DTMF tone problem

I have Verizon Home 768 DSL service. Verizon gives you a Westell 6100 modem, and the DSL shares the same line with my landline phone. I also have T-Mobile At Home VOIP. The VOIP worked great until a month ago. Suddenly, my 2 line answering machine no longer responded to incoming DTMF tones over...