Kindle Wifi $114 - you can use Wifi to browser internet and download the eBooks
Kindle Wifi+3G $139 - you can use both Wifi and 3G to connect internet and download the eBooks. You use 3G (on AT&T network) for free but it is slower that Wifi. However Kindle is used as a eBook reader not a tablet like iPad.
Usually eBooks are not free.
