Electronic NIV Bible and Hymnal from SAK Korea
Portable dictionaries are very popular in Asia, so it's odd that you don't see more reference texts in electronic form. Here's a natural choice: the NIV version of the Bible, displayed on a 3.4-inch LCD screen along with voice narration for those hard of sight. It even has a built-in hymnal!
While not a Christian myself, I have a fascination for bibles and an even greater one for hymnals. (I collect old editions of both.) I may have to put this model from SAK on the shelf next to the others once it's in the bargain bin.
And bibles in Korea? Turns out a huge segment of the South Korean population is Christian; they're not all Buddhist or Confucian by any means.
SAK electronic Bible [Coolest-Gadgets.com]

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It also has "MP3 playback, an integrated FM radio, recording, e-book support, and a SD memory card slot". While I am a Christian, I think I would buy this. Provided it has English language support, of course.
You mention the Christian population in South Korea...the largest Christian church in the world is located there..Yoida Full Gospel Church boasted a membership of more than 800,000 in 2006.
For comparison's sake, the membership of this church exceeds the entire population of San Francisco.
See:
http://en.wikipedia.org/wiki/Yoido_Full_Gospel_Church
Have you ever tried audiobibles? You can go to www.audible.com and download The Bible Experience, the whole thing now. I think that's a good example of one. I happen to be Asian and love Bibles and I collect them in different languages. I even had one in Korean until my friend moved to Korea, I gave it to him.
You collect hymnals? We must compare notes.* I've got some old Mormon hymnals with seriously weird hymns that have since been removed from the canon.
Me, I want a handheld electronic Missal.
(*The award for weirdest Protestant hymn would have to be a tie between "Great Speckled Bird" and the second (or in some versions, the third) verse of "Once to Every Man and Nation.")
Franklin.com sells a number of electronic bibles in addition to other electronic books.
I worked in a Christian retail store for about 11 years. These items were fairly popular, particularly around Christmas.