Spelling is the Achilles' heel of all word-based systems.
People who have trouble with spelling (such as non-native speakers of whatever language the words come from or children) may not be able to rely on word-based systems. Word-based systems are also going to be hampered by speakers of different accents.
Letter- and number-based systems are probably always going to be much more robust, especially when used with a standard phonetic alphabet[1]. There could even be a checksum letter/number to make the system even more robust. Unfortunately, such systems will never be as memorable or as easy to say as a few words (spelling issues aside).
People who have trouble with spelling (such as non-native speakers of whatever language the words come from or children) may not be able to rely on word-based systems. Word-based systems are also going to be hampered by speakers of different accents.
Letter- and number-based systems are probably always going to be much more robust, especially when used with a standard phonetic alphabet[1]. There could even be a checksum letter/number to make the system even more robust. Unfortunately, such systems will never be as memorable or as easy to say as a few words (spelling issues aside).
[1] - https://en.wikipedia.org/wiki/NATO_phonetic_alphabet