Amazon's Kindle series of e-readers is the most popular on the market. All models feature W-Fi wireless networking, but the more expensive models also include 3G cellular radios. These models can access the Internet, and the Kindle bookstore, from anywhere that with a cellular data signal. in the United States, the data access is free with a 3G Kindle purchase.
The Amazon kindle is now in its third hardware generation. The Wi-Fi-only version retails for $139, and the Wi-Fi+3G version retails for $189 as of March 2011. The Kindle DX is a jumbo-sized version of the Kindle, suitable for magazine or textbook-style reading. Its retail price is $37, but it does not have a Wi-Fi radio; its only wireless connection is 3G cellular service. Both the Kindle Wi-Fi+3G come with unlimited free Internet access, allowing you to download book from anywhere with a strong cellular signal.
Wi-Fi vs 3G
802.11 wireless networking, often shortened to "Wi-Fi," requires a wired internet connection and a properly configured Wi-Fi router. Most Wi-Fi networks are put in place in private homes, but many publicly-accessible "hotspots" are located in places like airports, hotels or coffee shops. A Wi-Fi router's range is about 50 feet. 3G cellular data is accessible in all urban areas in the United States and along most major highways. There is no need for specially-configured equipment with a mobile 3G connection; if you can receive a signal, you have Internet access.
Which to Use. Wi-Fi or 3G?
If you have the cheaper Kindle version, Wi-Fi internet access is the only means of connecting to the Internet and the Kindle store. You'll need to use your home Wi-Fi network or another access point to complete the initial setup and buy books. For the Kindle Wi-Fi+3G model, Wi-Fi is an option, but not a practical one: The book files purchased from the Kindle store are so small that they take seconds to download even on a slow 3G connection. The slow black-and-white screen makes the Kindle inconvenient for extended web browsing sessions. The Kindle DX can only use a 3G connection.
Which should I buy?
The mobile access of the Kindle Wi-Fi+3G is convenient, but is is worth the extra $50? If you have frequent access to Wi-Fi at home or work, the answer is no. Remember, the Kindle is a reader device, and the vast majority of time spent on it is reading books or periodicals. The amount of time most users spend actively connected is almost zero. If you can live with waiting until you're in range of a Wi-Fi access point, the lower-priced Kindle is a smart buy. If you don't have a Wi-Fi network at home and you're rarely in range of one elsewhere, the Kindle Wi-Fi+3G is worth the upgrade.