So it turns out that there are actually eight versions of the on-screen keyboard in Windows Phone 7 Series, as seen in the grid above. Like the iPhone, the keyboard will change depending on the application you’re using. For example, when in an email address field, you’ll get the @ key and .com, and when entering an SMS address, you’ll have easy access to the phone number layout.

Also, Microsoft stipulates how an OEM can integrate a hardware keyboard. Here are some details:

- All keyboards must have an emoticon shortcut key

- 12/20 key layouts are NOT supported (sorry SureType and T9)

- The hardware keyboard CANNOT be used to control the UI, meaning no D-Pads or arrows that move screen elements. That said, OEMs can use arrow keys to move the cursor

- Hardware keyboards CANNOT contain the following: ok/home, send/end, insert, control, alt, caps lock, tab, escape, or delete

(via: UI Design and Interaction Guide)