SQL/4GL INPUT from a form

How can I use place the screen cursor in a field at a locaiton other than the beginning of the field? For example I am requesting a US phone number. So the field is 9 digits long. If I already know the area code, I display it in the field and then perform an INPUT for the number. In these cases I would like the screen cursor to appear in the fourth position instead of the first. Thanks, Glen Johnson