DO I NEED A TELEPHONE LINE?

No, but you need a brain.

Depends upon what you use it for.  For instance, many house and health alarm systems need one.

If you want a landline telephone, I think much of Millennials and even more of Gen Z never had a non cellphone  

That's your decision, I personally have not had a landline since 2013, and even then 

basically kept it for wifi (not provided at an apartment where I lived part of that year) 

and occasionally for international calls (not covered in my cellphone plan at the time).

YES HOW ELSE WILL YOU TELEPHONE

NO, YOU DON'T.

You also don't need to SHOUT...

WHY ARE YOU SHOUTING?!?

Also no you don’t technically need it.

You need 17 of them. 

No, but you need a brain.

No, but you need a brain.