sentences:  While others have written text files about this device, and numerous software tone generators exist which claim to emulate it, it is unknown if any physical devices were actually built (including by Vail and Haflinger).Despite this, any blue box could, with skillful timing on the part of its user, be used as a green box.With the widespread phase-out of the ACTS signaling system, and indeed the long-completed phase-out of MF signaling in North America, the telephones for which this device was designed are no longer in service.