That's ideal and needs to be the first approach. In practice, people that communicate all day don't always understand than other jobs require uninterrupted focus. That's why engineers try things like no-meeting-wednesdays and schedule blocks for coding.

I wouldn't use the tool in question, but I relate to the motivation.

if you need to use this tool, the uninterrupted focus is most likely already gone, damage done. it's even likely that the person will return once your call is done to interrupt you again.

or.... they'll learn that you prioritize answering calls over f2f, and they'll start calling you all the time. easier to 'avoid' to some degree, but you're just shifting the interruption.

One thing often overlooked about work interruptions: interrupting one person's flow is usually to aid another's.

So as others have suggested the response can be prioritised according to importance and urgency.

While flow is critical for productive work, it should be directed to the highest priority tasks.

In construction we have a phrase "a dime holding up a dollar". It is up to you to decide if you are a dime or a dollar in each situation.

   please don't think I'm 
   being rude

By saying that you remind the interlocutor that being rude is in fact an option (indeed a widely used one) and you may simply be rude ... ah the subtleties of communication.

> no offence, but [offensive remark].

With all due respect, [respectless remark]

Sorry, not sorry.

I'm not racist but... [racism]

It's a great idea but...

yes, but no

But that particular remark wasn't offensive, no? Sorry, I'm not implying anything, just trying to understand your logic.

Can't speak for the others, but by merely saying "please don't think I'm being rude ..." you explicitly remind the other side that being rude is an option, and that what follows should not be taken literally. Indeed why would you say "don't think I'm being rude" except if you already anticipated that the other side will take it as being rude.

Trust me on this, I'm not lying to you ...

A small variation to this is to ask "Hey, sorry is it important?"

People tend not to think themselves or what they're doing as important for whatever reason.

It also sets the scene for future interactions. Oh and sometimes it really is important..

+1 to you friend, there is no problem in saying: can not now please. People will understand you.

+1. I don't understand why we need a Chrome plugin to act like an adult. Or, on the flip side, why you can't be an adult and not distract a co-worker. ha

might not work in all cases..

I think that would offend my British sensibilities. Unless delivered with a winning smile. It's amazing how much a smile can solve.