Just as a comment, your tests seem to show that reading your entire database (or at least the entire database for a particular area code) takes a fixed amount of time -- 30 seconds or so. So your goal would be to reduce the total amount of reading time, either by sorting the database files and doing a binary search, or saving that effort and using some kind of database to do the same thing for you. In either case, the goal is to reduce the total number of bytes checked for a failed search.