I ran a statistic two months back on all the say agains I heard in Europe. Guess what - 85% were misunderstood frequencies.
Hardly surprising with the mouthful of numbers needed for a frequency change these days - it takes a long time to say - a long time to read back and a long time to say again: "One three five decimal two zero five"..even when not combines with a "and inform heading" or even a simple "Goodbye".
With a suitable matrix all these frequences could be covered in alpha numeric form "change frequency to C-12 or E-15" etc. So how about a reasonable selector box standard to save the unneccessary chat?
Probably a pipe dream as long as we pilots and controllers continue to "hack it"...