After you have been granted an amateur (i.e. 'ham') radio FCC callsign you have the option to exchange it for a different one that is available and allowed for your license class.
I was assigned KM6AAI ...[ kilo mike six alpha alpha india.] I liked it but I wanted a shorter call by dropping the 'M' and perhaps getting a 'better' suffix. (I'm always amazed that the FCC gave out [kilo six alpha sierra sierra] and [whiskey four tango india tango])!!!
I wanted a 1x2 [K6_ _] but given how few come up for grabs and the competition for them, at my age I figured I would not get one in this life!!! So I decided I wanted a 1x3 ... [K6_ _ _]. I thought about a 2x2 [K _6_ _] but I find them hard to 'copy' as well as remember.
My goal was to find a callsign letter-combo that upon hearing was easy to remember as well as one that (subjectively) rolled off the tongue.
While my method was not scientific by any means, after talking to hams and non-hams and doing some testing I learned a lot of things. In no particular order, here are my findings.
I learned that people remembered a letter followed by a number [K6] better than two letters followed by a number [KM6], which reinforced my intent to get a 1x3 and and not the 2x2.
Given five sets of 3 letters (like what might be heard in a DX pileup) I found that my test group of people remembered the combinations with double letters [AAX] or where all 3 were the same [BBB] better than any other grouping EXCEPT if the 3 letters form a known word like CAT or DOG or GOD or GUN or BAT, etc.
All of the 'K6' three-letter common words [map, cop, etc] as well as the three-single-letter options [BBB, GGG] were taken so I had to look for a combination of double-letters followed by a third letter that would tend to stand out and be easily remembered.
I found that the better remembered groups were those that were easy to pronounce phonetically... they rolled off the tongue. Combos like [GGK... golf, golf, kilo] did not work as well as something like [AAL... alpha, alpha, lima].
I found that letters that were vowels or phonetics ending in vowels tended to sound better and be remembered better than harder consonants... 'alpha' worked better than 'hotel.'
I found that the double-letter pair coming first was better remembered than if the pair came last. [AAF ... alpha, alpha, foxtrot] was recalled more often than [FAA... foxtrot, alpha, alpha] because often people didn't hear the final letter of a double letter combo. They hear [FA] and not [FAA].
I learned that when the final syllable of the third letter rhymed or sounded like the final syllable of the combo pair, retention was increased.... like in [delta delta alpha].... all three end in an 'ah' sound.... [charlie, charlie, yankee]... all have an 'eee' sound. The combo of [golf, golf, uniform] didn't work as well.
I also learned that phonetics that had the emphasis on the first syllable (echo) were better remembered than when the emphasis was in the middle (november, sierra) or at the end (quebec, hotel).
While it was a very minor issue, I found that a two-syllable final letter phonetic like "echo" was more often remembered than a three-syllable third letter like [sierra ...see-air-ahh]. (There are only 2 one-syllable letters... golf, mike.)
I liked the sound of 'india' and while it is a three-syllable word, it gets slurred and often sounds like a two-syllable phonetic... 'in-jah.' It helped that 'india' is a well-known country.
I also liked the sound of 'lima.' While 'lima' is a city (in Peru and Ohio,) few people had ever heard of it. Perhaps if 'L' was phonetically 'lie-mah' (like the bean) it might work better than 'lee-mah!')
I gathered a lot of data. The argument can be made that it was just random and I won't dispute that. But random data is better (at some level) than a SWAG (https://www.acronymfinder.com/SWAG.html).
So at the end of the day... I decided to drop the 'M' and keep the suffix that the FCC had given me...[alpha, alpha, india] which was as good as I could get. Everything better was taken.
The above was MY methodology.
Fair Oaks, CA
"I am often asked how radio works.
Well, you see, wire telegraphy is like a very long cat.
You yank his tail in New York and he meows in Los Angeles.
Do you understand this?
Now, radio is exactly the same, except that there is no cat."
- Attributed to Albert Einstein