Google's phonebook can find US public business and residential numbers, and it can find them with less information than you need to look through the paper phonebook.

Google's phonebook is hiding within http://www.google.com. Occasionally, phone numbers will appear in the search results page, depending on the keywords you type into the search box.

To access the phonebook directly, type phonebook: before your search. This opens up Google's residential phonebook.

You can find someone's phone number, but you do have to give Google a little information. For personal numbers, you generally need at least a last name and a state. To find all the Smiths in Alaska, for example, type phonebook: smith ak. That's a lot of Smiths, and probably not very useful to find a specific Smith. If you know more information, such as the city you're looking for or the full name, type that in, too.

Limitations

Google's phonebook can only find public phone numbers. It can't find cell numbers. Quite often the numbers are outdated. I found two outdated phone numbers for a relative of mine, and his current phone number wasn't listed at all, even though it is public.

Reverse Lookup

Say you have a phone number and you want to find out who's number it is, such as from a message left on your cell phone. To do a reverse lookup, simply type the phone number into the main Google search engine, including the area code. Type using the format 555-555-5555 for best results. Google will still find the phone number if you use parenthesis around the area code, but you may also find some irrelevant results.

Remember, Google's phonebook doesn't contain any cell phone data.

Find Business Phone Numbers

Business phone numbers appear within Google search results, but they aren't as easy to access from the phonebook.