There are a few ways to trace a cell phone number, but it is important to remember that most methods will only work if the phone is turned on and in range of a cell tower. One way to trace a cell phone number is through the use of a reverse phone lookup service. These services maintain databases of phone numbers and their owners, and they can usually provide information on both landline and mobile numbers. To use a reverse phone lookup service, simply enter the cell phone number into the search box on the website.