engine - 11:09 am on Jul 8, 2013 (gmt 0)
I once had a client that would often take calls while we were in a meeting together. The result was that the meeting ended up going on a lot longer than it should. Additionally, after each call we had to recap on our discussion. It was intensely, frustrating.
I don't have a problem with someone saying excuse me, then take a call to let the caller know they will talk later. Of course, it's better if the phone is off during a meeting, but at a supermarket, my phone is probably switched on. However, I wouldn't hold a conversation at the checkout. Firstly, privacy is an issue, and secondly, if it's just chit chat with friends, it can wait.
I have overheard some conversations that go on, usually because the person has to raise their voice when talking on the phone. One person, I remember quite clearly, was having a discussion about what some z-list celeb wore at a party.
It was hardly important enough to inform the whole rail carriage.