What's the big difference between the two? I mean, the basics are understandable, with the 2G only having basic wap/edge Internet and the newer 3G and 3Gs having the more powerful and faster 3G support, but once you have updated a 2G with the new O/S software, 3.1.2, all models will do exactly the same thing!
For example, personally I use a 2G, and since doing the update on the software, it can do just the same as my neighbour's 3Gs, and is a fraction of the cost! Personally, with myself using the WiFi connectivity and the iPod, I don't need anything better. Even the iPod touch can do exactly the same as an iPhone, except from the capabilities of 2G or 3G connectivity, and obviously the phone!
So, basically, what I'm saying is, why spend out a few hundred quid on a brand spanking new 3Gs if you don't need it? Just get a 2G instead.
So, the moral of this story is, take a look at the specs of the different handsets before choosing what you want. I believe it could save you a lot of money.