wrong
"it's me" is technically wrong, but is widely accepted. the truly correct sentence would be "hello, it is i." the verb "to be" must connect two noun phrases of the same case. in this sentence, "it" is the subject of the sentence, so the correct pronoun should be the subjective "i" and not the objective "me." however, this is prescriptivist, and some people would debate it. sorry, adele.