PHONE NUMBERS: In the United States, the area code 555 is reserved for Directory Assistance and information numbers. Here’s an article that might help you as well as pointing out some potential problems (one of which Scott mentioned last time with the song “867-5309/Jenny.” I looked this information up by a Google search of “using phone numbers in fiction.”
EMAIL ADDRESSES: Since almost no rules govern an email address, there are no guarantees that you won’t stumble on a real one if you attempt to create a fictitious one. The only way to be safe is to create the email address you want (in gmail, hotmail, or some other free service) so it’s reserved. Just be prepared readers to try it, so you’ll likely want to check it periodically and empty out the email. On the other hand, you could use it for promotional purposes, if you have time on your hands to spend on such endeavors.
WEBSITE NAMES: The same issue apply to these as to email addresses. The only way to guarantee uniqueness and to avoid problems is to register the domain name you choose. However, website domain names are not free to register, but the cost through some registrars is minimal. Even more than an email address, a website could be useful for promotional purposes for your book(s). But be aware that as long as the book is out there, you should maintain the website registration. This is one reason you might not want to use a website in your novel.
If you already have your own website and want to be clever, you could always direct the reader to a special page on your website, and that way you wouldn’t have to pay separately for it.
Some years ago, a writer friend was working on a novel and wanted to use www.gotshot.com as a website where someone could find out how to treat a gunshot wound in the story (it was a humorous story). They registered the domain name and planned on using it for promotional purposes, but they haven’t finished the novel and I believe they let the domain name expire.
IP ADDRESSES: These have the same problem as telephone numbers, but fortunately some IP addresses have been reserved for use in fiction and movies, etc.
(Google: “using IP addresses in fiction”)
SOCIAL SECURITY NUMBERS (in the US):
(Google: “using social security numbers in fiction”)
As Scott cautioned, it’s best NOT to use unique personal identifiers such as a social security number in fiction at all.
CREDIT CARD NUMBERS: These are easier to use in fiction because of how they’re generated, and here are some interesting articles that will help.
The link below will let you check whether the bank identifier (the first 6 digits) on a given credit card number is currently assigned and to which bank.
Since not every credit card number combination is valid, and if you’re at all mathematically inclined, you can pick one that fails the MOD10 test described. Or, alternatively, take a valid card number and change ONE digit by one to make it invalid. For example, if the last 8 digits of the card number was 1234 5678, changing it to 1334 5678 would make it invalid (but please don’t use any of your own or anyone else’s credit card numbers for this purpose). Still, playing games like this, while interesting, is not a wise move. The problem is that, for VISA cards for example, many 4xxx prefixes will belong to some bank somewhere in the world.
For those of you who would like to play around, try this credit card number I made up: 4000 9988 7766 5544 (The Bank identifier 400099 is invalid and not assigned to any bank as of this writing).
You’ll find the MOD10 value comes up as 81, making it invalid and therefore would be a good number to use for fiction.
If you wanted to make it a valid number (one that passes the test), you would subtract 1 from the check digit (the last 4), making it a 3, so the sum ends up as 80, and therefore divisible by 10. Conversely, had this number come up as valid, all we’d need to do is change the check digit to make it invalid.
This is probably more information than most of you will ever use. I don’t recommend using credit card numbers in your fiction–unless you’re trying to craft some kind of mathematical mystery like Scott did in his second Jim hunter novel The Pythagoras Enigma.
BANK ACCOUNT NUMBERS: While these are less of a problem than other identifiers, you should still avoid them. If you really need a fake account number, you can either make up a bank name and assign any sort of number you wish, or if you need to use a particular bank by name, you can likely check online to find out how many digits are valid for that bank, then create a number that cannot possibly be valid.
SOCIAL INSURANCE NUMBERS (other countries):
PET REGISTRATION NUMBERS:
DRIVER’S LICENSE NUMBERS:
For these, do your research. If you really need a pet registration number and don’t want to get into trouble, then find out how many digits they would be in the location in question and add numbers or letters to make it invalid. Be sure you don’t just append these in an obvious way or it won’t hide anything.
Unlike addresses, which consist of multiple parts (street number and name, state/province, and country, remember that various ID numbers (like employee numbers at places of business) are designed to be unique. Tread carefully when using any sort of number that could be unique and could potentially identify a real individual or his/her property.
Even if you’re dealing with science fiction, futuristic, or fantasy stories where you can invent your own scheme of identifiers, it’s important to make sure you aren’t using a scheme that currently exists. Invent something with no chance of clashing with anything on present-day earth.
Ultimately, when in doubt, and if you can’t guarantee that you’re not linking to a real person, don’t use the identifier, or else find another way to represent it. And always be aware that some knowledgeable (or smartass) reader/reviewer could point out your “error” in creating an invalid credit card number, for example.
So, if you have your heart set on crafting numeric detail in your stories, have at it. But tread carefully.