There is/was a device called “FALSE ALERT” and it is used a lot in the Washington Beltway area. Here’s how it works:
The device resembles a beeper/pager, and is worn clipped to your belt, where anyone can see it. It’s not a real beeper/pager at all; it just gives the appearance of being one.
On this device is a button, and when that button is discreetly pressed, a beeping noise is heard, 30 seconds later. The owner of the device then uses that as an excuse to either exit a boring meeting, or end a boring telephone conversation, by saying, “Excuse me, but I must contact my office, right away. You know how these electronic leashes are!”
So, during a telephone conversation, you can utilize a device like that (or a genuine beeper/pager) to give you an excuse to end the conversation that is boring you, or otherwise wasting your time.
Just make sure that the other party on the telephone conversation hears it being sounded, so s/he will believe that your conversation has been, in fact, interrupted.
If you don’t have that kind of device handy, then another thing you can do, assuming you are speaking on a landline telephone, is to dial your own landline phone number, with your cellular telephone, and when you hear the click in your ear on the landline, say to the person to whom you are currently speaking, “Excuse me just a second, please; I have an incoming call.” Then, answer your “incoming” call.
Come back to your original conversation and say something like, “Forgive me, but my other call is long-distance and is of a ‘family emergency’ nature, regarding my cousin in Nantucket, Rhode Island. Can we talk later?”
The other party will excuse you, in both instances, to handle the other, more pressing matter, I’m sure.
Anyway, those are some things I have done in the past, and I’ve never had any problems being believed. The trick, of course, is to make the interruption sound genuine enough, that the other person on the line will excuse you to handle whatever the “crisis” may be.