das Telefon
telephone
A communication device that allows you to speak with other people over long distances.
Mein altes Telefon mit Wählscheibe funktioniert immer noch.
My old rotary telephone still works.

telephone
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telephone
A communication device that allows you to speak with other people over long distances.
Mein altes Telefon mit Wählscheibe funktioniert immer noch.
My old rotary telephone still works.

The word 'Telefon' (telephone) comes from Greek: 'tele' means 'far' and 'phon' means 'voice' or 'sound'. So a telephone is a device for hearing voices over a long distance.
Die Erfindung des Telefons hat die Kommunikation revolutioniert.
The invention of the telephone revolutionized communication.
The preposition 'an' is crucial: 'ans Telefon gehen' (to answer the phone; an das, accusative) describes the action of answering a call. 'Am Telefon sein' (to be on the phone; an dem, dative) describes the state of currently talking on the phone.
Kannst du bitte ans Telefon gehen? Es klingelt.
Can you please answer the phone? It's ringing.
The very common verb 'telefonieren' (to make a phone call/to talk on the phone) is derived from the noun 'das Telefon' (the telephone). It describes the action of having a telephone conversation.
Ich muss später noch mit meiner Mutter telefonieren.
I still have to call my mother later.
mobile phone / cell phone
'das Handy' and 'das Telefon' are both devices you can use to speak with other people. 'Handy' means a mobile phone that you carry with you. 'Telefon' is more general and can mean a cell phone, but also a landline phone in an office or at home. Learners may confuse the words because you make phone calls with both. If you mean the device in your pocket, 'Handy' is very natural. If the type of device is not important, or if it is a device on a desk, 'Telefon' fits better.

Auf dem Schreibtisch klingelt das Telefon seit einer Minute.
The telephone on the desk has been ringing for a minute.
Im Zug sucht Lisa ihr Handy, weil sie eine Nachricht schreiben will.
On the train, Lisa looks for her cell phone because she wants to write a message.