In terms of software, I've heard complaints on the 2G version (software crashes, phone freezing, etc.), though it doesn't exactly apply to every device.
Personally, despite the un-used features you'll be getting, I'd rather get something which is of a better make - upgraded. I'm presuming, as I don't have an iPhone, that the new generation of the iPhone should be of a much more improved device as compared to its predecessor (though I wouldn't say the same about Windows OS. But this is Apple we're talking about). Not only that.. You also will not be entitled to a software upgrade should you go for the 2G version, as updates now will only be available for the 3G version; despite having the same menus etc, both phones have different softwares altogether. I think a fee will be incurred should you want to upgrade your software.
Personally, I'd go for the 3G model. Unless, of course, you're on a tight budget, then the 2G wouldn't exactly hurt, though I have to disclose that I don't believe in old technology.
