This is a sort of spin off from answermachine post.
I share an office with two chaps who are not even in my department, they were just moved in with me due to lack of space in the building.
When they are not there, I will answer their telephones, just to stop them ringing, and will take messages, and they do the same for me.
However, I wish callers would not ask me if I know when or if they will be in the office. I don't know. It isn't my job to know, and they don't tell me. And vice versa. How can I put this politely to the next caller, who seems to think it amusing, or puzzling that I have absolutely no idea of their ETA? Pretend I am an answerphone?(I'd be tempted to blow a raspberry for the beep, or tone)