CallerSmart - CallerSmart is an application that is basically used for the purpose of looking up mystery phone numbers for free.
PhoneGenerator.net - Generate random phone numbers for all countries using the mobile phone generator. These numbers are fake, but they are built using the validations of telephone numbers.
Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
ThisNumber - ThisNumber helps you find phone numbers for people and businesses!
Sync.ME - Search over 1 Billion phone numbers worldwide. Identify unknown phone numbers and block unwanted calls.
ZabaSearch - Find people free with Zabasearch directory engine that includes free people search, reverse phone number lookup, address lookup, and more.