You will probably search through the yellow pages and try to find a name but it never helps unless it is a landline number. There are reverse cell phone directories you can use to track down these people just by using their cell number.
Doesn't the government have access to these mythical tools that give them the ability to find anyone, anywhere, and even find unlisted phone numbers, you would think so. Many people just straight to search engines and start frantically searching for the number in as many different formats that they can think of. It seems that directory assistance itself needs some assistance sometimes.
Of course, you'll also have access to home numbers, unlisted numbers, and business numbers too. Even with the free residential phone number search you can find out the details of which phone provider owns that number and in which city they are based and this may help you recognize the number. Above is one of the most reliable service's to use for reverse cell phone lookup.
Most of the services will offer you money back guarantees. Luckily, it isn't expensive, and provides you with options.