I'm sorry, I can't talk to you right now because I'm ..... another line. I'll call you back as soon as possible.
This is a companion discussion topic for the original entry at https://english.best/questions/17197,im-sorry-i-cant-talk-to-you-right-now-because-im-___-another-line-ill-call-you-back-as-soon-as-possible/
This sentence was clearly written in a time when we mainly used landline phones.
Some people ( like me ) still use land lines. I’ve never used a cell phone. I don’t even know how to make a call on one, although I doubt if it’s hard to figure out.
Well that’s not 100% true. I have two phones that someone gave me, but I’ve only used them as a camera. They aren’t connected to anything. I also helped an engineer do an experiment with a new feature for a cell phone.
The thing about being on another line is mainly for offices. Home phones VERY rarely had more than one line.