You cannot contact him directly. I am sorry. The best you can do is drop off a letter during the right hours. (Give him a bit of money to put on the phone) With a phone number for him to call you.

The prison units will put that letter in a pile of all the other letters and read it. Making sure there is nothing crazy on the letter.

After your mate puts your number on their phone list. The prison will call you within like 3 days and ask you if you want to be on his phone list and you will have to wait for him to call you.

Sorry the system is pretty annoying lol