If it's possibile, you should implement a "custom developer field", implementing this field ask the user for the name (eg telephonenumber).
You create a field type which is a copy of the textfield and in the form xml you put:
type = "telephonenumber" for the field
Create a file in the fields folder "telephonenumber.php" with the code of the textfield field.
In this way you simplify the work of the developer who will have to "only" change the code of the new field.