When it comes to cell phone numbers, the situation is completely different. The government created a lot of sophisticated regulations which are intended to protect the privacy of mobile phone owners as well as their identity. For example, it is illegal to collect cell phone numbers without consent of the owner, which means that upon registration, no data goes to any public database. Nobody, but the authorities, can figure out your personal details by a phone number, but as you remember, there are numerous places where you give out your phone number. You may not check the data receiver's policy on such data.
This means that you can allow such companies to trade your information with your consent, just by ticking a small checkbox.
Assuming that at least one such situation has occured, your data may be legally put in some private database. The company which obtained your consent became an operator of your personal details. They may even call you in order to check the accuracy of the information. You of course don't have any obligation to give them your details again.
This has allowed several companies to start providing reverse lookup services helping to find cell phone number owners. They simply buy personal information of as many people as possible and assemble it into one huge database. Such a database for sure will not contain all cell phone listings from the US, but usually cover around 40-60% of it. These companies have different plans for accessing their databases. Almost always you will be able to perform a single search, but then the price is rather high. It is always better to buy a package of several lookups or, for example, a monthly subscription. Don't worry that you will not use of all the searches that you buy because you can always help your friends reverse the cell phones they want to know or your family members may have phone numbers they want to find out the owner of.