The approximate setting of the movie was 1993-1994. After receiving his Cuban cigars from Stan the prison guard, Gacy Slips him money, a (20) twenty dollar bill which was the redesigned note that was not issued until 1998.
Phonecalls in and out of prison are all monitored.
Cuban cigars have been illegal in the US since 1962 and are still illegal in 2024.
The phone ringing in Jason's bedroom would have also been ringing throughout the house, waking everyone up.