If you discovered that the number in question is a mobile number, you should know that finding out private information such as full name and up-to-date address about the caller - will not be available online free of charge.
The top companies that offer professional databases invested millions to accumulate gigantic databases of mobile phone numbers - since records of that kind are not considered as public records and thus you'll need to pay a fee in order to get a reverse premium report about a cell phone number.

Before you decide to pay a fee, try to run a free reverse area code Trace to spot the city/state where the unknown caller is located.
This information can sometimes help you recall who owns this cell phone number - without the need for a premium reverse mobile trace report.