Various questions

I have the following questions:
1. If someone calls you at your phone number at the office and you are notat your desk at the moment, I pick the line for you. How should I say in English to the caller to tell him that you are not at your desk at the moment
(note: you are in the office)? Is it proper to say: "He is not at desk at the moment. May I know who's calling?" My query is on the first part of the reply.
2. If I am a smoker, I will say "I smoke a cigarette". If I am not a smokerand a smoker is smoking near me, the nicotine can still enter my body as if I am smoking. What should I say this kind of smoking (from my perspective) in English? Is it correct to say "secondhand smoking" (as a noun) & "I am taking secondhand smoke" (as a verb)?
3. Jane JAY and Michael PYE are a couple. It is correct to say "Mrs JanePye" and so if I want to mention both persons, it is correct to say "Mrs Jane and Mr. Michale Pye". But if Jane's name is unknown, is it ok to say "Mr and Mrs Michael Pye"?
Please advise.