A wireless telephone backup device for landline telephone equipment that may be located on the customer side of the landline service connection, typically in a restricted access location, such as an attic, basement, or utility closet. An interconnection circuit in the backup device detects service interruptions in the subscriber's landline connection and, in response, powers on a wireless communication device to provide backup telephone service to the customer premises equipment. The interconnection circuit also provides the other features standard landline telephone service, including dial tone, ring voltage, and normal dialing for outgoing calls. The backup device also forwards incoming landline calls to the wireless unit in the backup device, and may send a message notifying a maintenance center of the service interruption. Further, the backup device may initiate an indicator in an alarm system at the site of the customer premises equipment to notify the subscriber of the service interruption.