1 Jane Goodall: Time to use the Hotline.
2 Terry: A cell phone? That's never going to work here!
3 Rick: What, in London?
3 Terry: No, in 1940!
4 Yeti: {over phone} Jane! We've been trying to call. Where are you?
4 Jane Goodall: 1940.
4 Yeti: {over phone} Ah, that explains it.

Technically a hotline is a phone or other communication device that only connects to one specific end connection point, and that cannot be used to dial other connections.

An interesting related concept is the bat phone, which, according to Wikipedia, is a common term used to describe a business phone line that is only given to select customers or other contacts, and is handled with higher priority than standard calls to the business. I knew this sort of thing existed, but didn't know anyone called it a "bat phone" until just now when I was researching this.

A piece of business jargon coming from the superhero genre. That's pretty cool.

Sorry; it's bat-cool.