A device with these features and more is sure to exist some day. And there's no reason you can't stuff all this into a 3G phone, or a 3G phone into it . As cool as this idea is, the cost of design, manufacturing, and especially marketing will kill any chance of spending equal amounts for quality content. It won't be the Michelin Guide on these things, it'll be a warmed-over Yahoo or Travelocity or something without definitive content. It will be less than useless.
True usefulness is the great bugaboo of such high-tech schemes and outstanding ideas.
First of all, technologists seldom care about content because they're focused on the hardware and the idea. Second, great content such as the Michelin Guide tends to be entrenched in old formats that are difficult and expensive to transfer. And even if it was transferred, the model for scanning through the Guide is cumbersome. The best you could do would be to make the device like one of those electronic-book readers. Even that's cumbersome when you're flipping around a guide looking for something.