I could swear I'd written up a whole post about this, or possibly read one, but I can't find it, so...
JDC asks me how to format telephone dialog when you aren't meant to hear the offscreen character's voice.
Really, this is all about making sure the reader feels
the amount of time your onscreen character isn't speaking. I'll usually go with something like this (and forgive the HTML):
Joe picks up the phone.
No, I don't think so.
I SAID I didn't THINK so!
He listens, pacing, getting progressively more nervous.
Can't you for once gimme a break???
He slams the phone down.
You can use a line of action just to delay ("he listens") or to characterize the delay ("getting progressively more nervous").
If you just want a little delay, use a parenthetical -- (beat) or even just an ellipsis (...) works fine.
Note that just embedding an ellipsis in the dialog itself doesn't work well:
No, I don't think so. (...) I said I
didn't THINK so.
It doesn't really hold the eye long enough to give the effect of someone else talking. One key to writing transparently is not requiring the reader to think too much. He should just be swept along in the read. So often you'll find yourself unpacking moments on the page just so that they take longer to read -- white space is your friend there. When it comes to dialog, don't be afraid to make pauses where you need them. The reader isn't acting the lines out for you in his head, he's just reading like you'd read a book. So you have to make the performance happen for him in the blacks.
UPDATE: Ahhh ... alert reader Jason Sanders points out that John August recently answered this very question
. And with much better formatting than I, I must say.