Selecting All Numeric Values With Query String

What seems to be a simple question that I can not find the answer to. I have a form where if the user enteres values I want to return those values , if they do not enter a value then return all. ex: area code [973] - return all (973) or area code [ ] - return all area codes however, with a numeric field specified in the Access database, it seems you can not have a string like query = "select * from tablename where areacode = *"; how would i return all for a number without doing something like "where areacode > 0 and areacode <1000"? Thanks