What is a proper noun for telephone company?

There isn't one specific proper noun for "telephone company" as it's a general term. You'd need to specify the company you're referring to.

Here are some examples of proper nouns for specific telephone companies:

* AT&T

* Verizon

* T-Mobile

* Sprint

* Vodafone

* BT

Let me know if you have a specific telephone company in mind and I can help you with the proper noun for it.