Speaking English on the telephone is quite a skill. When you call a company and you get an operator, they might say things like:

Amplex Company, may I help you?
Good afternoon, the Amplex Company.

You, then, identify yourself:

This is Marcos Silva from the Oliveira Group in Brazil.
It’s Mr. Silva of the Oliveira Group in Brazil.

And ask the operator to connect you with someone:

Could you connect me with Marketing, please?
Could you give me George Stampleton, please?
Could I have Ms. Garth, please?

The person you want to talk to may not be available:

I’m sorry, he’s not in at the moment.
I’m afraid she’s out of the office.
I’m sorry, but there’s no reply from that extension.

You can always leave a message or say that you’ll call back:

Can I take a message?
Would you like to leave a message?

No, thanks. I’ll call back later.
I’ll call again at four o’clock.