Review: iPhone 3G
The SMS application has not been updated in any appreciable way.
The email application will support push email from Microsoft's Exchange server if your business permits it. It also supports remote device lock and wipe for the security minded, but this ony works if the device is tied to an Exchange server. The best improvement that most people will care about is the ability to download photo images from your inbox to the photo library of the iPhone. This is a nice touch to have. (You can also download and save images from the Safari browser. Just press and hold your finger on a picture, and the phone will ask you if you want to save the image.)
You still cannot send or view MMS messages, which for some, could be a deal breaker. AT&T has a web-based work around, whereby if someone does send you a picture message, you'll be sent an SMS with a link, user name and password where you can view an image stored on a web site. This is an extreme hassle and pretty much negates the joy that picture messages can create.
Otherwise, most aspects of these programs haven't been changed.