Windows Phone 7 comes with about 57 different input scopes you can use (there’s actually 62 or so, but 5 of them give an exception when loaded).  The two most important scopes are Text and TelephoneNumber.

• TelephoneNumber gives you the numeric keypad when the user goes to enter text.
• Text gives you word suggestions and smiley faces like in messaging.

Setting these in code is a little convoluted. It’s a lot easier to simply set it in the XAML, eg:
<TextBox … .. InputScope="Text" ></TextBox>

If you want to set the input scope in code, you need to construct an InputScope class instance, and add to it a InputScopeName class with the InputScopeName’s Value set to the InputScopeNameValue enum value.  It’s easiest to wrap this in an extension method:

   <Extension()>
   Sub SetInputScope(ByVal textbox As TextBox, ByVal value As InputScopeNameValue)
      Dim scope As New InputScope
      scope.Names.Add(New InputScopeName With {.NameValue = value})
      textbox.InputScope = scope
   End Sub

Then setting the input scope in code simply becomes:

 TextBox1.SetInputScope(InputScopeNameValue.Text)

Some things to note about input scopes:

• although you can cache an input scope, and assign it to a different textbox on an as needed basis, you have to be careful to ensure it is only assigned to one textbox at any given time. I doubt the memory minimization would be worth the effort.
  
• an InputScope can have multiple InputScopeName values, but it seems like only the first one in the list is used.
  
• the following InputScopeNameValue’s give a runtime error when run from the debugger:  PhraseList, RegularExpression , Srgs , Xml , EnumString

The main values you’ll want to use are:

abbreviated from http://msdn.microsoft.com/en-us/library/39D7932C-3E67-4142-9CCB-68843A571A66(v=vs.95,d=lightweight).aspx