Possible Duplicate:
Windows Phone 7 Search Button
I think that all Windows Phone mobiles have a search button (phisical or not).
Actually, they have three buttons: Back button, Windows Logo button, Search button.
Is possible to modify the function of this button (as Back button). Something like OnSearchKeyPress (as event handler).
Its possible?
This is not possible, because that could seriously alter the behavior of the phone. There is a search task you can use, for more info, see this MSDN article on it.