Right, stop what you're doing and listen closely.
If you go into a shop to buy something, or interact with someone behind a counter who is serving you in any way, STOP YOUR FUCKING PHONE CALL WHILE YOU DO IT.
Whether you're buying a packet of crisps from a corner shop or £300 of groceries from fucking Waitrose, STOP TALKING TO THE PERSON ON THE PHONE while you conduct the transaction.
You can do this in one of a number of ways. You should be able to work some of these out, but in case you're one of the people who thinks that conducting a transaction with someone without even acknowledging their existence other than to wave a tenner at them with your precious fondleslab cradled in your shoulder is an acceptable way to behave, I have to assume that it's possible these haven't occurred to you:
- Say to the person on the other end "Hold on a moment, I have to pay for something" and drop the phone, still connected, into your pocket. This way you can pluck it out again once your business is concluded and continue right where you left off.
- Say to the person on the other end "Hold on a moment, I have to pay for something, I'll call you back" and end the call. Conclude your business, then call them back. They really will understand.
- Just cut the call. Then when you've finished your transaction you can call them back and choose whether to tell them the truth (again, they'll be very understanding as long as you weren't actually in the middle of guiding them step-by-step through an open heart surgery procedure) or just say "Sorry, the call dropped, not sure what happened there. Anyway, where were we?"
There are more. Honestly, I reckon you can come up with a few more if you try.
The important fact here is that you fucking do it. It is so unfathomably rude not to, I can't understand how people have the gall to do this and make it through the rest of the day. Thankfully I haven't worked behind a counter since mobile phones became omnipresent, but if I did I would refuse to serve anyone who didn't even manage to pause their conversation while expecting me to serve them (like they do at one of my favourite pubs in London).
Really. Just say "Hold on a sec, I'm at the bar" or "One minute, got to pay for my shopping, I'll ring you back" and then speak to the person serving you as if they are an actual human being with their own feelings and thoughts.
Because, in many ways, they are.