you don't need to worry about that unless your using eBay or something like it, all stores like F.Y.E. and Best Buy, get the new ones, and don't sell the old ones
Iphone 3g is the newer one, in the US at least, they don't sell the 2g one anymore. 3g = mobile wireless access for internet + email + things, and it's faster than EDGE or a "2g" data connection. It basically means you can surf the web faster than a device that lacks 3g, however, wifi mode is naturally faster than the 3g.How do I use this Iphone 3g that is from China?