In New England people use contractions:
Can't, shouldn't, didn't.
This can make it difficult to interpret when any other obstacle is present like an accent, over a radio and muffling. A lot of times my conversations will happen like this:
Me: Did you take care of that thing?
Them: I didn't.
Me: You said you did or did not?
Them: I didn't
They emphasize in the unhelpful part of the word. So I sometimes think they in fact did take care of that thing when they have not.
Also people refuse to learn a phonetic alphabet. Especially in the IT dept you should already know the similar sounding letters and understand the need to be clear. It doesn't even need to be the NATO phonetic alphabet, just something that separates D from C, E, P and T. Once when reading out PPB, I said "Ponies, Ponies, Bravo!" Silly, but I was understood.