I guess it most not be totally obscure though, becuase "In Illinois, it is commonly shown to classes in home economics, for whom it illustrates the concepts of responsibility and deviancy."
Looking at Amazine, the second movie, The Severed Arm, looks easy to find, if not inexpensive. It also appears to incorporate more than one urban legend, since the title comes from the one where a bunch of people who are trapped together each give up an arm to eat.
I listened to a podcast on the Janett Christman story and yeah, the only thing it has in common with the phone call story is that a babysitter gets killed. They did mention that Evelyn Grace Hartley is alot more famous. Janett Christman is technically unsolved in that there was never a trial or conviction, but even at the time it was very clear who the killer was. The police botched it by fighting over juristictions, weirdly interrogating the suspect at a private residence in a way that probably would have caused problems if it went to trial, and taking a polygraph test seriously.
The presumed killer Robert Mueller probably also committed another rape and murder that someone else got the gas chamber for, and a number of sexual assaults that someone else went to prison for on a conviction that was overturned after a few years. Both of the people convicted for the other crimes were black. The one who was executed definitley did kill his own wife, for which he would have had a 15 year sentence. The other guy became a suspect after some Peeping Tom charges and confessed because the police threated said that if he didn't they'd just let people lynch him (which is how his grandfather died).