All of them are used by native speakers, but (B) is the correct choice in terms of formal usage. It's the long form for "Speaking".May I speak to Miss Dolly?
(A) I'm Miss Dolly.
(B) She's speaking.
(C) Here's Miss Dolly.
(D) Hi, it's me.
In other words, "I'm . . . " isn't the usual response, but it is used.Hello, this is Corinne. (NOT USUALLY...I'm Corinne)
"Speaking" is also short for "She's speaking" or "I'm speaking".'Could I speak to Jane Horrabin?' 'Speaking' (OR This is Jane
Horrabin (speaking).) (US This is she.)
But they are indeed used by native speakers all the time. It's synonymous with, "The person you are looking for is speaking." In other words, "the person" is a singular noun, its pronoun is "she" or "he", which gives, e.g., "She's speaking."I can't think of any example people will answer like "He's speaking." or "She's speaking."