Massachusetts becomes fifth state to make prison calls free

Technically, a jail is for people not yet convicted, and prison is for the convicted. In practice, a lot of people just use the terms interchangeably.

and are housed interchangeably in big cities where most of the population experiences these facilities

Jails are also often used for people who are convicted of lesser crimes, with sentences under a year.

This is not correct. Yes, jail is people waiting for trial and usually convicted people with less than a year sentence. Prison is usually for people with a year or longer sentence. My state has a prison for younger drug offenders and other places for violent convicted criminals.