The lookup cell phone number service allows a user to find the name and address of the person from whom they receive a call.  This helps to contact them at a later stage.  This feature has loads of features.  But the choice of the right service is most important.  Most look up directories are paid ones.  The free service providers do not contain all the numbers.  The reason is that the free service providers do not update their database regularly and also do not contain the list of unlisted numbers.  The details of new numbers are never seen to be found.  The reason why a cell phone directory is not being put up is for privacy concerns.  This becomes very advantageous when it comes to the calls from the telemarketers.  There are plenty of companies which believe in telemarketing their products and services.  So, publishing the number would be not proving to be a good idea.