I think the Curve is a fantastic email device. If you've got multiple accounts, the push email of the Curve is very nice. I find the UI of the Curve to be a bit cumbersome and the menu structures are neverending. If email is your thing, the Curve is great. Excellent keyboard and they did a great job with the form factor.
As far as third party apps, I haven't done much with third party apps on the Curve. I've dabbled mostly with freeware. With the iPhone, I expect a very high level of app. The combination of a powerful OS and large userbase makes it great for developers. Now, distribution will be exclusively through Apple. It still remains to be seen if Apple will hinder development of "official" apps in anyway.
Now, as far as the iPhone is concerned:
- Safari is heads and shoulders above all the competitors
- Email on the iPhone will be faster with 3G
- Navigating multiple accounts is a bit difficult
- Expect developers to "fill in the gaps" where there are UI issues, albeit minor ones
- It works flawlessly with your Mac
- If you p/u the new iPhone, you'll have the latest and greatest
- At the end of the day, it's the best iPod.
Web apps never really took off. The real apps should be spectacular. If you have any old Palm apps, StyleTap will be releasing emulation software that will you to run all your old Palm OS apps.
Really, they are both great devices. I was surprised at how much I liked the Curve. That being said, the iPhone is more of a complete package.
-Chris