The more you adhere to standard phraseology, the better off you'll be.

I work at a large airline and at the start of a trip I find myself flying with someone I've never seen before more often than not. On the first flight, each pilot is assessing what/who they've got to fly with for the trip. I get a warm fuzzy when the other guy contacts departure and says, "Departing two thousand one hundred for one one thousand," as opposed to "Two for eleven".

Thank God international flying is in English. There, rigid phraseology discipline is non-negotiable if you want to ensure a smooth flight experience. Zee-roe, not Oh.

Ben, well said. :D

Very well said, Ben, absolutely spot on .

The complicated issue is that traditionally domestic US is treated outisde international regulations inside the US and that is very visible in R/T phraseology.

When deregulation started, US pilots flying 98% of their time inside the US were thrown outside their borders and exported the bad habbits. That is fortunately no longer much the case, but bringing and mandating ICAO phraseology inside the US still is an issue today.

Alfanumerics, is not a EU thing, but a European Airline thing. There is no regulation for it, it is voluntary. Was introduced by Air Inter in the 80's to differentiate themselves from Air france after a few incidents and similar call signs inside the same company.

From my past experience the most incidents were with similar call signs inside same company , BA1428 and BA 2428 etc.. for this the random alphanumeric is very good.

For an incident between 2 different airlines , there is no real solution . Even if as ATC you spot one ( e.' BA1428 and DLH 1428 in same frequency at same time , it is very difficult to change , as flight plans are published and repetitive.

ATC cannot durably change a call sign on its own ( only inside a sector ) as call signs are what is the reference ID to ATC systems along the route and used for Route charges collection and overflight diplomatic celarances.

A very old problem, looks simple to fix, but it is not.
Sticking to standard ICAO phraselogy and carefully watch out for your call sign is currently the best solution.

Right,ATC. We had a morning hour years ago,when we had too many with very closely numbered,approaching and departing the same airport. Bad planning from our traffic office,but how could they know? By walking to the next floor and asking. -511,thank you.551 left heading xxx.515,direct xxx.512,to approach.215,to control. All this within every other traffic at busy morning. Some guys down there on the screen were just great.

Eurocontrol call sign similarity program
 

https://www.eurocontrol.int/services...ty-css-service


https://www.eurocontrol.int/tags/call-sign-similarity