[NiLuJe]

With a DX US, no, you'll have to use a hack (usbnetwork, or have someone whip up a simple date hack).

And no, if you use any of the recent hacks, neither jailbreak nor usbnetwork should cause any trouble regarding official updates/reg status.

The only thing I can think about is that it may not stick, since we'll just be overriding the date, without really changing the timezone. (Unless someone out there can find me a DB of the TZInfo files used by the Kindle, because it's not the usual format of the ones used in a full GNU/Linux system, and there's no local DB)

With a DX GW, you'd have the choice to try some other carriers to check if one of them provides timezone info, but with a DX US, I don't think you have any other choices. (I may be wrong, I'm not that familiar with the US models).