If you don't want to switch to AT&T or pay an ETF, and the iPod Touch gives you literally everything the iPhone has minus the phone, then you'll buy the Touch. That's exactly what I did, until I decided that I was tired of carrying two devices.
The iPT does not give you the same features as the iPhone for the simple fact that it only has WiFi which significantly narrows it's usefull operational area. If you are not in range of a wifi network, it's nothing more than a device with the ipod app (including podcasts + books etc.) and games, as the greater percentage of usefull apps need some sort of internet connection. Sure, there are apps that don't require internet and are usefull, but my point is that the iPT does not equal or replace the functionality of an iPhone.
And if you don't need or want a permanent internet connection, I think you are not in the targeted market of iPhone buyers in the first place, and this is why you bought the iPT, because at that point when you bought it, you did not need the phone part of iPhone, which proofs my point: people who need or want a phone buy an iPhone, people who do not need phone and/or permanent internet buy an iPhone... those two scenarios do not interfere