I have practically the best smartphone technology of 2004 right here on my desk! (ah, 10 years ago, i was probably still fiddling with my dad's PDA)
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With a whopping single core 312 MHz Intel XScale PXA270, 32 MB of flash memory (no longer loses data when the battery dies!) as opposed to using RAM as storage, a beautiful 2.7" 320x320, 16-bit TFT resistive touch display, a 0.3 MP camera, an IR port, Palm OS 5.4.8, and 2G connectivity! But wait! There's more! At a svelte 0.9" thin, it features a full-size SD card slot that requires a tweak to accept 4+ GB SDHC cards, but it also takes Wi-Fi cards! Not to mention the stock battery stacks in at 1800 mAh!
(admittedly, it probably wasn't the best it could be, don't think Palm really figured out thin back then)
10 years from now? Hoo boy, I'm not expecting transparent phones or anything star-trekky, but I don't think I can really predict it. Although I would guess they'd be very similar to phones today as we bump up against the ceiling of diminishing returns.
Unless a giant paradigm shift occurs, something that puts the original iPhone's unveiling to shame.