Recently there was an article about Harper Collins bringing public domain ebooks to the NDS.
http://technology.timesonline.co.uk/...cle5303730.ece
BTW, that cartridge can be pre-ordered on Amazon UK.
http://www.amazon.co.uk/100-Classic-.../dp/B001LK6XKE
While reading about it, I've come across several different readers. I'm using this thread to list them all.
http://www.dcemu.co.uk/vbulletin/showthread.php?t=68172
http://sourceforge.net/projects/ndslibris/
http://www.dcemu.co.uk/vbulletin/showthread.php?t=68172