I'm sorry guys but you aren't even talking about the biggest upgrade! When I made my first phone call today on the 4G it was crystral clear and way better then the 3G or 3GS! The speakers are louder and the screen is worth more then the price of admission. If your gonna spend more then a 100 for a 3GS then just save a bit more and get the 4G. It blows the 3GS out of the water I'm sorry!
I guess, but honestly, I'd feel guilty if they release a 5 next year that is much better than the 4. I don't feel guilty or upset going from the 3GS to the 5, but going 4 to 5 would irritate me in the same way that going 3G to 3GS would have. Like I said, I had many things I did not particularly like about the i4, so it was personally a no brainer for me: either wait weeks for an i4 or get a good phone right now.
As for call quality, I've not had any problems with my 3G in the past. Don't know about the 3GS as I haven't really made more than a phone call or two with it.