Use NumberGuru to figure out who keeps calling you

NumberGuru is a free service that allows you to quickly look up who is calling you, in some cases even if they are calling you from a cell phone. The best part of the service, besides its speed, is the ability to reverse look up as many numbers as you want for free.

You can use NumberGuru either by visiting the Web site, or by downloading and installing either the iPhone [iTunes link], Android or Windows Mobile [Zune Marketplace link] app.

Once the app is installed, it's as simple as entering a phone number, including area code, to find out who has been calling.

After a seconds you will be presented with the name and location registered to the phone number, as well as any comments fellow users have made regarding the phone number.

According to the app description, NumberGuru covers 100 percent of telemarketers, roughly all landlines, and an estimated 50 percent of cell phones. Verizon Wireless is the only carrier listed as not included in results.

Between attempting to look up foreign numbers, as well as reading through the app reviews, NumberGuru appears to only work with U.S. phone numbers (for example, looking up an 800 number in Mexico failed to return any results).

The mobile app also includes the capability to add a NumberGuru Top Spammer contact your address book. The entry will include the top numbers that have been reported as spam to the service, updating itself each time you run the app. Should someone with one of those numbers call you, you will be able to quickly see that answering the call would just be a waste of time.

NumberGuru is necessary app, even if you just use the Web service; being able to quickly look up random phone numbers that keep calling you comes in extremely handy. The comments left by other users often times clear up not only the name of who is calling, but why they are calling.