Not only was I lucky enough to get Pokérus in Crystal, but it also happened to be just before arriving at the Indigo Plateau for the first time. This provides a rather unique opportunity.
Within the Indigo Plateau is an old man NPC with an Abra who only appears while you have not yet beaten the Elite Four; this NPC can use his Abra to Teleport you back to the door of your home in New Bark Town. This disrupts the usual programming for Elm’s Pokérus phone call, since Elm is programmed to call you immediately after you step out of the PokéCenter that diagnoses your infected Pokémon (sidenote: The healing NPC in the house on Route 26 does not diagnose the Pokémon nor does she disrupt the script).
Using the Abra to teleport to New Bark Town allows you to take an extra step or Fly and then take an extra step upon landing before Elm calls you. This allows for the already rare phone call to take place on a number of otherwise impossible tiles. Anywhere just outside your home or at Lake of Rage normally would be impossible, as would one step away from any PokéCenter. I included the screenshot at Olivine City specifically since it seems to have the closest interactable tiles relative to the Fly landing tile; unfortunately, you cannot select Surf in time before his call after taking the one step, but I’m curious if you have any suggestions for where to Fly to in order to disrupt this sequence further.
You can walk into your home and any PokéCenter that you Fly to and Elm won’t call you while you are indoors; however, once you exit the building, you no longer have this extra step and he will call you.
I found this fringe anomaly interesting and thought maybe it could be explored further.
