fruux - Free service that takes care of your contacts, calendars and more so you don't have to.

Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.

FullContact - Put the power of full contact information into your web or mobile apps.

WhosCall - WhosCall is a reliable caller ID app whose popularity has led to its adoption by many users including international media. You can now manage the numbers calling you regardless of whether they are part of your contact list or not... read more.

Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.

CallApp - Free Caller ID & Call Blocker app that allows mobile users to block phone calls, identify calls, blacklist unwanted callers and much more.