Thank you for your question. Your third option was the best, and I'll explain why.
When someone asks you "Can I talk to Jeremy?" (and he is not there) you can choose to apologize (this is usually polite) and if reasonable, tell the person WHY they cannot speak to him.
So the conversation would go like this:
- Hello, can I talk to Jeremy?
** (you) I'm sorry, he's at lunch.
- Oh. When will he be back?
(you) In about 30 minutes.
- Okay, I'll call back then.
(you) Great. Have a good day.
- You too. Bye.
** One last thought: If it seems inappropriate for you to tell the caller where Jeremy is, it is totally polite and reasonable for you to say "I'm sorry, he's not available" and the person should understand that they are not granted the knowledge of where he is. This is a common response in a business type setting.
Hope this helped you.
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