The application for your computer, Blackberry, etc. is free. You just download it. You don't even have to own a Kindle to do so. It's just a different reading experience than the Kindle. The Kindle is superior to those and has better user interface.
3 G means that your Kindle has its own wireless internet connection in it like a cell phone. It will automatically connect with
Amazon so you can get your books pretty much anywhere that has the capability of having cell phone transmission. (Don't ask me about international usage. I think there used to be additional fees. I don't know if there are still additional fees.)
The Wi-fi version means that your Kindle doesn't have a 3G cell phone style connection. With that device, you have to be at a Wi-Fi hotspot OR at a computer to get your books onto your device. You can't just download a book while traveling down the highway or out in the wilderness camping (You can with the 3G device). Instead, you have to be somewhere that has Wifi "or" you can hook a cable to your computer and download the file and transfer it over that way.
The 3G connection is the most user friendly. It is easier to use.
If you only read a few books a month, then the cheaper Kindle is probably an acceptable choice. If you are a person who reads a few books a week, then it's worth the extra $50 to get the 3G.
I've downloaded books while at campsites on the side of a mountain, while driving down the highway, while in bed, while...well, you get the drift. I don't want to have to be tied to my computer or a wifi spot.
We will be a two Kindle household soon. My son is getting one for Christmas from his father. Shhhh. (I also have the Kindle App on my Blackberry but it's really for when I get stuck in a line. I can pick up a book and read then. I don't like using the Blackberry to read books. Not enough screen space. I also have the Kindle App on my computer. I almost never use it.)
