Doctor Channel

The "Doctor Channel" was a channel created by the Unified Intelligence Taskforce as a connection to the Doctor, giving him a contact line directly to HQ. It was presumably created early in the '70s. Kate Stewart, leader of UNIT, doubted that he even remembered it, due to him never using it.

During a crisis of "frozen" planes in the air, contacted UNIT on the channel via her device with a text that Mike decrypted. Missy used it to tell them she wasn't dead and they should meet her with armed soldiers. (TV: The Magician's Apprentice)