The information I have for the same points is that there are two models of Kindle 3rd generation, one that handles both mobile network browsing and WiFi browsing, the other model only does WiFi. Both will work anywhere. Regarding the power adaptor, they are all multi voltage.
If you are considering a 2nd generation Kindle then watch out because that came out in two models, one that only works in the USA, the other anywhere. I have first hand experience of that.
Note that, in the above, "anywhere" is not to be taken literally because no agreement for free 3G browsing exists in some countries while you can browse for free in others. You can of course pay and browse, but just how you do that I am uncertain.
The source for this info is REO Technology Ltd. who specialise in Kindle repairs. I believe they would respond to an enquiry for further detail.