What is a (Local Exchange) Prefix?

The first three digits of a seven digit phone number in the North American Numbering Plan are called the "prefix" or "exchange". In some areas, you are limited to a small set of prefixes determined by your physical location. This is because -- in the old days -- the telephone network used these first three digits to connect an incoming phone call to the right "central office" where other electrical hardware would then interpret the remaining four digits. Basically, this type of network layout, a hierarchy, made telephone networks cheaper to build and maintain.

Even though most modern telephone networks being build and upgraded today are so flexible that such restrictions are no longer necessary, telephone companies continue to use the old conventions. In future, you will be able to get any prefix in just about any area code, no matter where the actual telephone is located (as is already a the case with internet based telephony).

Which is the best prefix to have?

When it comes to vanity numbers (phone number mnemonics), some prefixes are better than others. This is because different three-digit combinations will be more or less likely to represent the first three letters of a word. For instance, 18 words start with the letters associtated with the prefix "592" and 353 words with "92", while there no words in the english language starting with the letters for "555" and only 23 with "55". You can use our Prefix Comparison Tool to compare the vanity number potential for local prefixes.

In general, if you are trying to get a phone number with good vanity phone number potential, prefixes containing 1's and 0's should be avoided, as should prefixes with consiting only of 7's and 5's, since these numbers only map to consonants.

If you stuck with a certain prefix, you may also be able to ask the telco's customer service representative if certain numbers are available. Use our Prefix Search to get a list of words for your prefix.