receiver (n)
/rɪˈsivər/

the part of a telephone that you hold close to your mouth and ear

fax (n)
/fæks/

a machine that sends and receives documents in an electronic form along telephone wires and then prints them

mobile phone (n)
/ˈmoʊ·bəl foʊn/

a telephone that does not have wires and works by radio, that you can carry with you and use anywhere

public telephone (n)
/ˈpʌblɪk ˈtɛləˌfoʊn/

a telephone, usually in a public place, that is operated using coins or a card

phone card (n)
 /ˈfəʊn.kɑːd/ 

a small plastic piece that is used to pay for calls from a public phone

code (n)
/koʊd/

a system of words, letters, numbers, or symbols that represent a message or record information secretly or in a shorter form

number (n)
/ˈnʌm·bər/

a word or symbol that represents an amount of quantity

call back (phrasal verb)
/kɔːl bæk/ 

to phone someone again, or to phone someone who called you earlier

ring (v)
/rɪŋ/

to (cause to) make the sound of a bell

message (n)
/ˈmɛsɪdʒ/

a short piece of information that you give to a person when you cannot speak to them directly

dial (v)
/ˈdaɪəl/

to operate a phone or make a phone call to someone by choosing particular series of numbers on the phone

look up (phrasal verb)
/lʊk ʌp/

to seek information

hang up (phrasal verb)
/ˈhæŋ ʌp/

to end a phone conversation

get through (phrasal verb)
/ɡet θru/

to make contact with someone by telephone

available (a)
 /əˈveɪ.lə.bl̩/

able to be bought or used

hold (v)
/hoʊld/

to wait until you can speak to the person you have telephoned

extension (n)
/ɪkˈstɛnʃn/

an extra telephone line connected to a central telephone in a house or to a switchboard in a large building

tone (n)
/toʊn/

a sound heard on a telephone line

answer (v)
/ˈɑːn.sər/

to say, write, or do something as a reaction to a question, letter, etc.

speak (v)
/spik/

to talk to someone about something; to have a conversation with someone