Many people in the earlier days have faced of calls/messages coming from unknown person who don’t provide their identity and trouble you.
The problem is resolved by True caller.it has almost 90% of the numbers information.For truecaller to function properly you need a data connection, .it may be 2g or 3g.
Depending on your data speed it will provide you the name of the unknown caller when the call arrives or after you end the call also you can check the details.
Truecaller functions by taking contact information from the phone of all the people who have truecaller installed.and then by checking the combination of which name comes in maximum contacts it puts out the name in the app.
Yes there is 1 concern that there is security breach as you wont want people to get your niumber but it can happen that with truecaller they are able to do so.