You can agree to pay for them at a given prices via email or slack. It’s more or less guaranteed that contraband will get into prisons if someone is willing to pay for it. Thus the rules around no cash or phones for prisoners.

Inmates are treated very differently by the legal system than regular people. Thirteenth Amendment: “Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States”