According to wikipedia, "In the event of an emergency deorbit that would
bring the Orbiter down in an area not within range of a designated
emergency landing site, the Orbiter is theoretically capable of landing on
any paved runway that is at least 10,000 feet long, which includes the
majority of large commercial airports. (In practice, a US military airfield
would probably be preferred for reasons of security arrangements and
minimizing the disruption of commercial air traffic.)"

So, for all you ATC types out there, how does this work? Does NASA just
pick up the phone, call JFK Tower, and tell them to expect the shuttle in a
few minutes? Do you guys get any training on what to do should this ever
be required?

I imagine it would require moving a lot of flights out of the way pretty
quickly.