Very simply, to communicate when the distance between them is too great to speak face to face. But sadly, on more than one occasion, I have observed two dummies, while side by side, communicating with each other on cellfones !!! I guess they thought it was "cute," and their parents must have had more money than they or their kids had brains. It's an extremely useful and quick means of communication. Before the telephone was invented (and became widespread) people were dependent on mail services for communication over distance. Even if the mail service was efficient, just imagine the time for a short postal message to travel by surface from, say, a small place in Maine to another small place in, say, the Mississippi Delta!
People use telephones
We use telephones to talk with. These days, people use cellphones .
People today can use old telephones ( 2012 ) but they are most likely rare.
Not many people used it because it is expensive.
because they hate telephones
Telephones are about instant communication with other people wherever they are.
They used to send letters 5o the people they wanted to talk to.
Through things such as skype telephones have become unnecessary for some people who live of the internet. Though for many a telephone is still central so the use has only been changed in some situations. Many people still consider the telephone superiour.
something you use for telephones
You pick up one end, dial a number, and listen. They're used as communication devices.
By mail
you call people with the telephone