Plus all the shortcomings, there is no guarantee that 3G will always work, rather, work that he would, but it's possible that amazon may limit access, for example, only to its Kindle Store for message traffic, as I understand it, it passes through their servers (if I'm wrong, please correct).
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Although, frankly, sometimes you want to have access to places where no wi-fi, though surfing on a kindle and not very comfortable, but read the same Habr.
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In the end, if the extra 50$ you do not strain, take the 3G, but to use it you'll most likely rarely (except at first).