Not all versions of Windows Mobile 5 are the same. Aside from the differences between the Pocket PC and Smartphone versions, you also have differences based on which AKU version your device is running. AKUs are Adaptation Kit Updates and they are issued by Microsoft to OEMs to deliver additional features or fixes required for a particular Windows Mobile device. For example, an AKU could come with new drivers.
The site msmobiles.com has posted a picture-heavy look at AKU version 3 which comes with support for auxiliary displays on clamshell Smartphones, a new Account Set-up Wizard for email, WPA 2 encryption support, SMS over GPRS functionality, and full video scaling support, and plenty of bug fixes among others.
You will need to check with your device manufacturer to see what AKU version they offer for your device. You can also find your current AKU version in the About screen by looking at the build number (the first number is the build and the other digits will be the AKU version).