UPDATE: The launch turned into a nightmare. The AP reports that the demand for new iPhones, and the release of updated software for the original iPhone overwhelmed the iTunes Store. The Apple Support boards are filled with angry comments from new and old customers who wound up with an iBrick instead of an iPhone. Would I like a new iPhone 3G? Absolutely. It's cheaper than the old one (at least initially), but for the time being, the first generation iPhone will have to do.
First, 3G speed. It ain't here (at least in Mobile). AT&T told me on July 1 that the new, higher internet speed "should be operational by the end of the month". (Will customers have to pay the higher price for data, even though 3G isn't available?) So, if you expect to get faster, over-the-air internet service immediately, you will be disappointed.

Two, battery life. In watching
Walt Mossberg's review on The Wall Street Journal website, he claimed that while accessing the 3G network, the iPhone's battery drained by the end of the business day.
Three, text messaging is no longer included in the monthly rate. With the older phone, the price included 200 text messages. (Maybe AT&T's "Family Rate" will cover this. I haven't seen if it will, or it won't).
Yes, call clarity is supposed to be phenomenal, and the App Store feature will expand the iPhone's use almost beyond imagination. But, when it comes to this iPhone, iPass, at least for now.