Has this ever happened to you? You know someone, you know their name, but for some reason you didn’t get their mobile number. You know they have a cell phone because they showed it to you, but when you try to look them up using a phone book or online “Yellow Pages,” their name is nowhere to be found. And there you are asking “how can I find someone’s cell number?”

As you will have found out, if you did what was said above, there is no telephone directory of cell numbers. Due to various federal regulations related to privacy, all cell phone numbers are not listed to prevent data extraction by telemarketers and others. While this minimizes cell phone spam, it makes it increasingly difficult to look up someone’s cell phone number.

So what do you do when you face this problem? Fortunately, there are several options available when it comes to looking up mobile phone numbers.

Your first two choices will cost you nothing more than some time, patience, and less than ideal performance of those two things. In other words, free doesn’t necessarily translate to a high success rate. On the other hand, it doesn’t hurt to try because you never know when you’ll get lucky.

The fastest of the free cell phone number lookup methods is to “Google” the person. It really can be that simple if they have left some personal information about themselves on a website somewhere. Social networking sites like MySpace, online classified ad sites, and message boards are the most likely places to return someone’s name, address, and phone number.

Your second option when it comes to free cell phone number lookups is to use one of the free cell phone directories that can be found on the Internet. There is a catch to using one of these free sites. To join, you’ll need to help them fill out their database of names and numbers by entering your own cell phone information before you’re allowed access. This method is slowly gaining acceptance among mobile phone users, but these databases are far from complete.

In most cases, the best way to find that unknown cell phone number is through a national registry of cell numbers. These websites charge a small membership fee, but it may be worth the cost for the time savings alone. You’ll also get unlimited searches for the life of your membership, and if you have an Internet-enabled phone, you can access the site from your phone. It’s like having a portable phone book wherever you go.

So the next time you’re wondering “how do I find someone’s cell phone number?”, here are three ways that should be able to help you. Just remember that there are over a billion cell numbers and the method you choose will have a direct bearing on how successful you are.