“There are 6 unambiguous 1-letter vowels”―since when are vowels in English unambiguous? English writing should properly be classified as logographic, since you can't know how a word is pronounced from its spelling, or vice-versa.
Has the author ever communicated his own middle and last names in a phone call? A big benefit of numeric identifiers in the first place is that it's easier to dictate them without error. Even in my native phonemic language, with words or letters it's too often back to the Folks' Phonetic Alphabet: “No, D as in Dmitry.”