How Area Code Correction works.

The fastest way to build a complete understanding of the area code correction process is to examine the history and correction problems associated with a single telephone number. Along the way, you will be introduced to the complexity issues that will enable you to build a rapid understanding of the file and database correction process.

Correcting a single telephone number

We will use PhoneSeal Desktop Professional to illustrate the actual correction process for a single number. This is a free download. get yourself a copy here.

In the window above, we are following the correction history of the number (415) 373 1983.

The (415) area code is in the San Francisco Bay Area. From the correction possibilities above, you can see the first split occurred in 1992. If the number was in existence before 1992, then the area code would have changed to (510) in 1992.

The objective of splitting out these numbers to new exchanges was to leave the number available for re-issue in the old area code. So, sometime after 1992, the number (415) 373-1983 was re-issued to somebody else inside the (415) area code.

Time passed. By 1998, the (415) area code had again became overburdened, and the number (415) 373 1983 split out yet again, becoming (650) 373 1983.

Since 1998, the (415) area code has been able to re-release the number (415) 373 1983 for yet a third time!

Meanwhile, the (510) area code had become overburdened, and needed to be split. So in 1998, the number (510) 373 1983 became part of the split, and moved to area code (925).

So the original number (415) 373 1983 could have three possible ambiguous outcomes, depending on it's date of issue.

If it was issued prior to 1992, then today it would be a (925) area code.
If it was issued between 1992 and 1998, then today it would be a (650) area code.
If it was issued after 1998, it will remain a (415) area code today.

This introduces an important concept: ambiguous numbers, or ambiguity. Ambiguous numbers arise where there is a date range within which there have been more than one area code split. For example, if you knew that the number you were correcting was issued in 1989, then you would not have any ambiguity. If the number worked in 1989, then today, it must be (925) 373 1983!

However, if you know that the number worked sometime between 1989 and 1994, then you would have two possible outcomes. If it was issued prior to 1992, today it it would be area code (925). If it was issued between 1992 and 1994, then today it would have the area code (650)

To resolve ambiguous numbers, we use a second internal database, which contains information on Zip codes and area codes.

In the example above, the Zip code associated with this telephone number is 94550. The Zip code 94550, according to PhoneSeal, today has the area code (925).

So if you have an old phone number, (415) 373 1983, and you know that it's associated address is in Zip code 94550, then you can say with certainty that the number today will be (925) 373 1983.

We now have the pieces to be able to explain the file correction process.

Correcting entire files

Most file correction of telephone numbers is based around name and address files, which contain details of the customers' addresses, including Zip code, as well as the telephone and fax numbers.

PhoneSeal is based around two internal databases. The first is a complete list of all the changes and splits to area codes since 1990. The second is a "Zip code-to area code" database, which we use for verification.

In the above example, you can see there were three possible outcomes for a single telephone number, based on it's date of original issue. We call these multiple-outcome optional numbers "ambiguous numbers".

Date Ranging

Now if we knew the telephone number was working in 1995, it would not be ambiguous. We would know that today it must be in the (650) area code! But if we could only say that the date range was somewhere between 1990 and 1999, then we would have an ambiguity issue. It could be any of the three options, (415), (650), or (925).

So the wider the date range you choose, the more ambiguous numbers (or correction alternatives) you will generate. We need a way to choose the correct number from the possible numbers that PhoneSeal finds from the internal splits database. This is where ZipChecker comes in.

ZipChecker

To do this, we use our second internal database, ZipChecker. It looks at the possibilities from the splits analysis, and compares that with the Zip code. If there is a match between one of the ambiguous options, and the current area code that ZipChecker indicates, then we can correct the number. If there isn't, it remains in the ambiguous number report.