I had same problem. There are two places to plug phone into on Xfinity modem/router "tel 1" and "Alarm/tel 2". I discovered today when modem was relocated to a higher point in our home to improve WiFi capability, we did not realize we plugged phone line into "alarm/tel 2". If this is your problem, put phone line "tel 1". Afetrwards, the only way to check is to call landline from a cell phone and leave a message or have someone call you and leave a voicemail. AFTER PLUGGING BACK INTO "Tel 1" our stutter dial tone worked AND landline display showed "new message". Phone did work in alarm/tel 2 but we lost voicemail notification features by having phone line plugged into the wrong place on the modem/router.
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