I was less confused by that since I read, "Sono io," as, "It is I," for reasons I cannot explain. I am more confused by why "mi" is not accepted. Sure, it's poor grammar but if the Oxford English Dictionary accepts poor grammar as gaining legitimacy through repeated use by most of the English-speaking population (e.g., ending sentences with prepositions or using double negatives), then shouldn't I be allowed to end a sentence with the wrong pronoun? That question is, of course, rhetorical. I know I'm wrong but I'm tired and I wanted to use the internet for what it was intended: complaining about silly things.

yes, it's true. Italians are likley to say "sono io" when starting a phone conversation for instance, or "sono Federico". Always sounds odd to Brits who are are likely to think "of course you are you", of course you're federico. you nit - do you go around with a name badge to remind yourself :) . But as apviper says it's just the Italian way of saying "It's me", "It's Federico"

like "who broke the window?" "sicuramente non sono io"