Jails generally provide paper and pencils for inmates to write letters. They also have something called "indigent mail" which is a program offered to those inmates who've not received any money in their commissary trust accounts. The jails are pretty understanding and humane when it comes to inmates staying in touch with loved ones.
https://www.inmateaid.com/ask-the-inmate/how-do-inmates-get-paper-and-pencil-stamps-and-envelopes-to-write-back-if-they-have-no-money-in-there-account-in-jail#answer
Accepted Answer Date Created: April 20,2014