A: Hello! May I speak to Bob, please?
B: He's not in.
A: May I leave a message?
B: Sure. Go ahead.
A: This is Tom. Please ask him to call me back as soon as possible.
B: OK. Bye.
A: May I speak to Mr. Wang, please?
B: Who's calling, please?
A: This is Tom Lin.
B: Hold on, please. (a few seconds later) He's out at the moment.
A: When will he be back?
B: I don't know.
A: OK. I'll call back later. Bye.