This read-create DisplayString holds the ISDN calling address assigned to the second B channel of this signaling entry, in a row that augments the standard ISDN-MIB signaling table. An admin sets it, per the vendor's own description acknowledging this isn't an ideal design, when the second B channel on a Basic Rate Interface needs its own distinct calling number. Setting isdnSignalingCallingAddress2 to a second DID number lets the device present the correct calling address when placing or receiving calls on that second B channel.