Listed numbers are very easy to trace without the power of the internet, you can use phone book but for the case of unlisted numbers, there are numbers that are not listed in phone book and there probability of being trace online is very small.
A good example of these numbers are mobile phone numbers.
Fortunately, there are number of ways to lookup unlisted phone numbers but these steps are considered try and error as you are not sure of the results obtained but can be a good starting point.
Some of these easy steps are visiting volunteer site where people willing submit there contact information but you will be unfortunate if the number has not been listed.
Another good way is typing the number in search engine.
You are expected to type in the number along with the area code, this will help make the search more specific.
The good and best way is investing a token to directories that have gathered the required information you are searching from the person name, location, workplace etc.
Why paid directories are considered best in unlisted phone number lookup is that they help you put the information in place and most of these directories update there information that will best suit your demand.
It all depend on you to choose the right directory as choosing a directory to undertake the task of unlisted phone number lookup is sometimes very tricky and require some skills.
Looking up unlisted phone numbers is very easy, it only need a fee which I consider small to the amount of information that will be expose to you.
Therefore, choose the directory that best suits you.