If you plan to sell the phone or if the menu is hopelessly glitched, a factory reset is your last resort. According to the :

The only downside? The CS2051 lacks a backlit keypad. If you need to dial in the dark, you’ll want a CS6114 instead.

If the phone emits a continuous low beep, a missed call is waiting. To retrieve the final message, dial #-9-1- from the base unit. The message will play from the last date of service.