While not a full evaluation, this is a quick overview comparing the 3D graphics power of all three of today’s mobile gaming platforms.
While the iPhone 3GS is significantly faster than its predecessor, it definitely has a long way to go before it can catch the PSP. However as the DS (and Nintendo in general) has shown, you don’t necessarily need the best graphics to have the best games.
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HCW is Comparing Specs: iPhone 3GS vs PSP vs DS