Todays fast and complex internet means we have access to any info we need. People are always looking for a simple way to find out about people or businesses. Companies earn money by charging the people who are looking for records. The sort of info people look for varies, peoples info such as names, phone details, cell numbers etc, but there are all sorts of research details that can be found online.
Companies like this use the web to sell themselves, rather than offline methods because their customer base is also online. Traditional research companies do exist away from the internet of course but their service is more complex. Private investigators like those we see on tv cop shows are the nearest thing offline, providing similar records and services, but can be expensive. Reverse lookups from websites are popular because people dont wish to do research themselves. Google and social networking sites are also useful for research, but many times you will just see adverts for the same businesses.
If you need to research a cell number, such services can help. reverse lookup can offer info such as who phoned you, and also carrier details, and this mkight help point you to who has been potentially harrassing you.