I heard an interview with the guy who created
it the REAL one and his daughter. He knew there
was no way for anyone to record it, and as people
pointed out here already, cell phones are incapable
of producing it.

BUT: It did lead to the idea of people using
a PC based sound generator to create the highest
possible frequency that the phones could generate.

It turns out that about 1/2 the teachers in the
school could not hear it, and it seemed to be
a sure thing after age 40.