e reader - difference between wifi and 3g?

The wifi versions can only access the internet (including the Kindle store) if they're in range of a wireless router or hotspot. The 3G versions can also use a 3G (mobile phone) connection as well as some of the older mobile technologies. You can access the internet via 3G, but you can't download stuff that's been emailed to your free Kindle account. You will however get a message to say that you have items waiting to be downloaded once you're connected via wifi. If you need to download emailed items via 3G you'll need to pay for them (it's a few pence, but I've never used it). Books you've bought from Kindle will download free via 3G.

In easy terms-- 3G makes use of the same varieties of alerts as phones, so which you could get internet at any place Wifi requires a router inside the area, as good as being equipped to use it with the password (except it is a public community)

3g kindle has all that functions, you can use it surf in wifi.