Or when they're walking somewhere?
Or half busy doing something else?
I don't know why, but it irritates me and I find it soooooo rude.
A bloke to do with work just phoned me - it was about a project, so not just a 'chat' IYSWIM, and first of all he was walking somewhere, so all breathless, and saying 'hang on a moment, I'm just crossing a road' and then it became obvious that he was at his son's school, and there was lots of background noise/shouting and I could hardly hear him, and then he stopped mid-sentence as he was clearly attending to something else...
Is it just me, or do you think it sends a message of 'this conversation isn't important enough for me to sit down and give it all my attention, so I'm fitting it in around other (more important ) things'?
He obviously thought he was being really efficient in HIS use of time, but wasted much more of MY time!
I also find it really rude when you're talking to someone in the passenger seat of your car and they stop the conversation when their mobile rings to have a long chat with the person who has phoned them. Unless it's an emergency etc, in that situation I'd always say 'can I give you a call back, I'm with X at the moment'.
Also, dare I suggest that it's blokes who do this more than women??