Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
ReportedCalls - ReportedCalls helps people search and identify potential spam and scam phone numbers.
CallApp - Free Caller ID & Call Blocker app that allows mobile users to block phone calls, identify calls, blacklist unwanted callers and much more.
USCallers - USCallers.com is a free, reverse phone lookup service for both cell and landline phone numbers.
CallerSmart - CallerSmart is an application that is basically used for the purpose of looking up mystery phone numbers for free.
Reverse Lookup - This iOS App helps users identify the caller based on the phone number. If any user receives a phone call from an unknown number, they can use this App to look up information on that caller.