Input is must for any application and valid input provide best result which you want.
Windows phone 7 having SIP ( Soft Input Panel) for input.
For example phone number should be numeric always personal name having alphabets only such kind of validation is required when we develop any application.
With windows phone 7 we have facility that keyboard automatically change according to input scope.
For example if we want numeric value in textbox than it shows numeric keys.
Below are the some patterns which windows phone support. AddressCountryShortName
You just need to add Input scope property to textbox and rest of the validation for input handle by Windows phone 7.
The SIP (Soft Input Panel) change according to Input scope.
For more detail see below screen.
You can download the code at https://skydrive.live.com/?cid=1eda2012469ff8ad&id=1EDA2012469FF8AD!243
Thanks & Best Regards,