VTech's Power Fail back-up system lets you make calls during a mains power interruption with your cordless phone. During a mains power interruption you can supply the power stored in your handset battery to the base unit, so you can make calls even when the power is out. DECT technology giving digital clarity, range and security. Wireless (Wi-Fi) Network Friendly. Calling Number Display Call Block allows you to block unwanted PRIVATE and UNAVAILABLE calls plus the Call Block List which allows you to block incoming calls from up to 20 specific user programmable numbers. Main base unit desk or wall mountable.