text: Mike: Can you give me a call when you're free.
  John: Sure thing. I can't talk at the moment as I'm in a meeting.
  Mike: When will the meeting finish?
  John: Not sure.
  Mike: Approximately?
  John: I really don't know.
  Mike: Look I really need to speak to you tonight.
  John: I'll try to call you but I can't promise anything.
target: John can't talk at the moment as he is in a meeting. John doesn't know when the meeting is going to end. Mike needs to speak to John tonight. John will try to call Mike when he's free.