Please be wary of Persona 2: Innocent Sin spoilers in this post.
[ Maybe you overheard it one day on the way to class, or from some students who were gossiping idly away in the streets, nothing better to do in their spare time.
Either way, the things you heard were mostly the same:
"Have you heard about that game?"
"What, the one where you call your own cell phone number after doing some silly ritual?"
"Yeah! That's the one. It's supposed to summon Joker-sama, who will make whatever you want reality."
"No way, that's a load of crap, right? No one can do that kind of stuff, it's just an urban legend."
"Is it? I heard from a friend that her cousin in Sumaru City played the Joker game and summoned him and she became an idol, like she'd always wanted!"
Maybe what you overheard plays on the edge of your mind. Maybe it's just so odd a rumor and so many people are talking about it that you just can't help but wonder if it's true. It could be idle gossip, of course. Maybe you tried it to prove that there was no way this rumor was real.
Either way, it seems you've decided to look into this. Maybe you have free time, maybe you secretly want your dreams granted--either way, you were pointed toward Kasugayama's students, who being in Sumaru and having recently improved their school from delinquent to prized status, seem to know more than they let on.
The first boys you talk to aren't much help, but when you talk to one of the students who apparently came and skipped school from that place, you're in for a curious conversation. ]
[ ooc: Two things! 1) You can have them just directly call Joker himself, or 2) You can have someone meet Jun (anywhere, it's likely he might travel around Japan a bit, after all) and talk to him. ]