My dad is reading the novel Once Gone and there are several paragraphs as follows:
To her relief, Bill's voice came over the phone.
"Hello," he said.
Riley's heart jumped. She didn't know whether to be relieved or terrified to hear his voice.
"Bill, this is Riley," she said.
"I know who this is," Bill replied.
What we (my dad and I) learned was we should say "I know who that is," not "who this is."
Although I can't tell why, I feel "I know who this is" is also correct. It sounds like "who this is" focuses on the speaker (in this case, Bill). Although Riley was on the other end, when Bill was holding and talking to the phone in his hand, he was imagining the phone to be the representative of Riley. Because the phone was on Bill's side, it was OK for him to say "who this is".
So my questions are:
- In most cases, do native speakers still say "I know who that is"?
- Is it OK to say "who this is"?