public
office
The office telephones were all out of order.

cellular, cordless, digital, mobile, portable, wireless
radio, satellite

use
Can I use your telephone?

be on
Don't pester me now—I'm on the telephone.
We're not on the telephone, so you'll have to come around to the house. (BrE)

have
Excuse me, do you have a telephone?

answer, get (informal), pick up
Hang on—I'll just get the telephone.

hang up, put down
She put down the telephone and burst into tears.

call sb to
He was called to the telephone just as he was leaving.

bug (BrE), tap
connect, install
disconnect

ring
The telephone was ringing furiously.

number
All letters should include an address and a daytime telephone number.

book, directory
bill
call, message
conference, conversation, enquiry (BrE), interview, poll, survey
contact
She is in telephone contact with headquarters.

helpline (BrE), hotline, support
The charity has set up a 24-hour telephone hotline.

company
banking (esp. BrE), service
charges
cord, handset, headset, receiver
cable, line, pole (AmE), wire
exchange, network, switchboard, system
operator
booth, box (BrE), kiosk (BrE)
tapping

by telephone
Can I get in touch by telephone?

on the telephone
She sounded very distant on the telephone.

over the telephone
I don't want to talk about this over the telephone.

Telephone is used with these nouns as the object:
ambulance