The Gameshark 2 contains a product called DVD Region X. Region X kills the region lock on the PS2 by loading and blocking it before you load the DVD -- I think. Anyway, the GS2 should work for playing DVDs from any region.
As for Japanese PS2s only playing region 3 DVDs, I think NCS is confused. Japanese PS2s play only region 2 DVDs, unless you use Region X or a Gameshark 2. Region 3 is non-Japan parts of Asia, I think.
I've not had any experience with playing foreign DVDs with a GS2 or Region X, so I'm not sure how well it works. However, it ought to be a worthwhile purchase.
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