You can either check the details of any arbitrary number or check the numbers from your call logs, which are not in your contacts list.
* Unlike other apps, this app DOES NOT upload your contacts to any server.
* This app requires a WiFi/3G connection to work efficiently.
* Please note that some numbers may return 'Unknown number'. This is expected behavior. But for most of the numbers you should get the details.
Details of permissions:
* Full Network Access - To query our online database
* Read Call Logs - To check your call records
* Read Contacts - To find those number in your call logs which are not in your contacts