My husband carries on a conversation, feeling that he needs to best friends w/ these callers. Me? I'll let them know in no uncertain terms, that I'm not able to talk right now; or this is a good one.
I tell them that I'm going to another room, "would they mind holding on for a minute? and I'll pick up the other line. I set down the phone and don't hang up. Then I go about whatever business I was up to. I think they get the hint and hang up. Either way, I'm done w/out being rude because my dinner hour was interrupted!