When you click a Windows Phone 7 TextInput control, the Virtual Keyboard is shown!
There are many techniques to disable it. I will tell you my technique now:
Change the property of textbox as seen below:
IsHitTestVisible="True" (in XAML)
or
textBox1.IsHitTestVisible = false; (dynamically)
This technique will disable Virtual Keyboard.
As dheeraj warned me: you might need to install new patch of WP7 Tools here
This method might not work with RTM.
Hope it helps!