Works on all Korgs as it is an intrinsic part of the OS...Details are in the manuals. Page 179 of the PA2 Manual, 161 of the PA3 manual and just look in the Songbook reference section for the other manuals as I do not have them to double check exact page numbers.

There is even a very small free applet that does it for you, PAsCO. Can be d/l from Yolasite website

http://korgpa2xpro.yolasite.com/jackpote-pasco.php

Which creates the very small midi file needed to select a songbook entry. All that needs to be done is link this midi to a chart in the iPad app...

I use Unrealbook as it is one of the VERY few iPad chart (PDF) reading apps that allows the linking of these midi files. It cannot play "full" midi files as it is not specifically a midi player as such, but it can send these as it is a one bar entry only and requires no timing pulses or clock references.