For RDMLX - See the lansa source of reusable part LREX0052 for examples of Datatypes
There is a parameter on TextBoxes called Datatype
By setting the value to 'Number' you can make the keypad show numbers.
#Com_Owner.Set_TextBox Name(ZIP) Layout_Col(2) Layout_Row(2) DataType('Number') Value(#uZip)
For RPG - Run the Longrange demo and go to Introductory Examples --> KeyBoard Data Types (Shipped example EXAM0052)