It's really stupid to buy the 3GS model. Even if you don't need the upgrades it has...
a.) Resale Value. I guarentee that whenever you get rid of your iPhone, sell it on ebay/craigslist, the new iPhone 4 design will be valued at more than $150 higher than the old iPhone 3G/3GS design. So this $100 you save now will cost you in the long run.
b.) The reason for the poor resale value, lack of flash, 720p video recording, video calling, front facing camera, pentaband antenna that makes the new iPhone usable with the new standards globally where as the old standards werent, 8gb vs. 16 gbs, A4 processor, four times the resolution, new design etc etc.
c.) Tell you what, if you really want the 3GS, PM me, order the 16 gb iPhone 4 and I will ship you my 32gb 3GS in mint flawless never once been dropped condition plus the $100 difference in the price tag + the zagg skin I've had on it since the day I got it + a leather case + $50 profit for you in exchange for the iPhone 4. You get a 32gb 3GS mint phone for the same price as what the 8gb costs you, some extra accesories, and even make a $50 profit!