"would you care to elaborate Rojash?"
The
kindle 3G allows you to access the Amazon site and download books via the 3G mobile network. The 3G also comes with wifi.
The wifi version allows you to access the Amazon site and download your books via wifi. In neither case does Amazon charge you for the download. (Think about it - if they let you download from a mobile network that they are subsidising, they are hardly going to charge you for downloading when using your own resources.)
If you don't have the 3G version you can download via your own internet/wifi connection or you can use the free wifi available in many cafes (such as Starbucks) and other places. You can (of course) also connect to a paid for wifi connection like those that you find in some hotels and internet cafes.
You can also ddownload books direct to your home computer, and transfer them to you
kindle using the USB cable supplied.
Some people find the 3G connection worth the extra money, some don't (I don't ). But in any case the cost to you of a download from Amazon is entirely free.