I have an answering machine that is set up to answer calls. If that doesn't pick up (because of a power outage or something), then it goes to comcast voicemail. I prefer to use an answering machine and have comcast voicemail as a backup. The problem is that once I switched from AT&T to Comcast, my machine doesn't detect hang ups and records 30 seconds of dead air. I come home to multiple messages of dead air. This didn't happen with AT&T. Suggestions?