Everytime someone joins it, their entire phone book and/or facebook/linkedin contacts etc. (if you give permission) are stored in their database. At the moment, there are 8 million users, so if there are an average of 100 contacts per person, that's 800 million contacts in their database. If anyone who has your number in their phone book has the app installed, then your phone number is already in their database. If i type your number in the app, it will show me the name by which that person has stored your phone number.you cannot search by name but only by number. I find it very useful because whenever I get a call from some automated advertising thingie or some other spam call, it automatically shows that because someone or the other has stored that number in their phone book.