Unpublished telephone numbers are those that are not published on phonebooks or telephone directories. Usually these are cellular phone numbers while rarely they can be land lines. The reason why they’re not published is two fold.

In case of cell phones, they are automatically unpublished. There exists no "Cell phone directories" or "Cellular Phone Books". The reason is simple…..to keep the unwanted calls that may cost you time and money away, including telemarketers.

In case of land phones, they WILL BE automatically published or listed on phone books like the one you get from AT&T unless you make a special request that the number should not be published. And certain people do opt their landphone numbers out of telephone directories just so that they keep the annoying telemarketers away among other reasons.

However, this doesn’t mean that mobile phone numbers are not published anywhere at all. They are listed on special phone books that are only availlable to the law enforcement authorities. If you fall in trouble, or if you make troube, they have access to these directories so save you or to frame you! However, the general public has no access to these phonebooks unless they use a service such as that offered by Lookup Unlisted Phone Numbers Read more about Unlisted phone numbers here.