If someone keeps calling you and you'd like to know who it is, there are plenty of options for finding out. Whitepages, a reputable phone number lookup site, has contact information for over 90 percent of U.S. adults. Plus there's Google, which can turn up a surprising amount of information in a few simple clicks. If you need to find the owner of an unlisted number, you can also do that for free. It just takes a little digging.

Navigate to the Whitepages reverse phone number lookup page. Pop the 10-digit number including area code into the search field to get the owner's name and address. If you don't score any hits, head over to Zabasearch. This website claims to have more residential phone records than Whitepages, so it might turn up a match. Both sites offer free lookups for listed landline numbers. If you want to connect a cellphone number to a name, however, you'll generally have to pay for the premium service.

Cellphone numbers are not listed in any public phone directory, and you'd usually have to pay to access private carrier records. However, National Cellular Directory lets members of the public look up cellphone numbers for free during a one-hour window each day. "Happy hour" times vary, but if you sign up for a free account, the company will tell you when the next session will be going live. You get two free searches during each happy hour. Simply type in the number for instant results.

If a person has paid to de-list his phone number, it's usually because he doesn't want it to be found. That's where Pipl comes in. This directory searches through databases, social media platforms, forums and other registration-required sites to find information that other search engines can't reach. If the person has listed his phone number anywhere on the web – even behind a pay wall – Pipl might just find it. You just need to enter the telephone number in the search box and wait for the results. The algorithm is designed in such a way that it will give you all the information tied to the phone number, such as the owner's name, address and employer.

Perhaps the simplest way to find out who a phone number belongs to is to type it into a search engine like Google, Yahoo or Bing. If the number belongs to a business, the owner's name will almost certainly appear toward the top of the search results. For private numbers, you might turn up a match if the person has posted the phone number online – on a personal bio or resume site for example. Since it takes only a second to input the number, it's certainly worth a shot to find out who the number belongs to.