Truecaller allows you to connect your phone to a large crowdsourced directory of phone numbers and contact information with your iPhone. The result is a powerful tool that can help you determine who called when you miss an inbound call, where a phone number originated, and much more just by checking the directory.
When you set up Truecaller for the first time, you will be prompted to set a few basic options and then verify your phone number, whether you want to integrate your contacts into the list or not. After verification, the free account allows you to look up numbers from more than a billion crowdsourced entries of businesses and individuals around the globe. The directory contains a wide array of numbers including landlines, cell phones, and even some prepaid cell phones. You'll gain access to anything someone adds to the directory , which makes this a very powerful tool in any of the more than a dozen countries in which it's available.
Truecaller is a free app but does have a premium option that allows you to see who has viewed your profile, while removing the ads and providing additional contact requests for your account each month. The app is very powerful with or without the upgrade, but if you are a true power user, the upgraded features will make it that much better.