Tao the ghost can hear all Robert's reasonings in his head. He knows that Robert is starting to see that this technically could not be Nitte.
Tao then says to Robert, "Tell Jack, keep Nitte talking. Let her or whoever the person is keep texting. Ask some more questions."
"OK. Let me explain to Jack first."
Even though Robert is sitting next to Jack, Robert continues to text Jack: "I really don't think this is her, precisely because she says she is on a flight. Take a look at it yourself. Her message is sent by a mobile phone network, which is impossible if she is still flying."
Jack thinks on that. That is very odd. He does see that when he was typing and sending the message, it did say "SMS" which is sent by mobile network.
"What should I do then?" Jack texts back.
"Why don't you send a message to her and say, who is this? Or ask something that only she knows or only she can do. See what she responds."