Windows Phone has an on-screen keyboard. We call it the SIP (Software Input Panel). It appears when users give focus to a TextBox. The configuration of SIP keys varies by how the developer sets up the TextBox’s InputScope property.
Here are three configurations (mango has 57):
On the far left is the DIGIT configuration. Remember, SIP configuration is meant to be an aid to the user, not a validation tool. Users can still use a physical keyboard to type in alpha characters, or use the clipboard to paste. Even with DIGIT, letters are possible.