Hackers can use your cell phone number to determine your name, where you live and work, where you travel and when you sleep.  They could also listen to your voice messages and personal phone calls. Most people have been told to keep their Social Security number private (and they usually do).  However, they do give their cell phone number freely. 

Smart phones have become more powerful..  These phones contain contacts, e-mails, credit card details and bank information.  Most phones contain a global positioning device that can be used to track locations.

Once a hacker has a phone number, he/she can easily determine a name by taking advantage of the Caller ID system.  Using special software, a hacker can "spoof" a call - make a call that appears to the phone company as though it's coming from your number.  They can then call themselves using your number and watch as their Caller ID device lights up with your number.  Attackers could theoretically do this with thousands of numbers to create their own personal mobile phone book.

When you download apps from your cell phone provider, you could download malicious apps (even though the major vendors check carefully before posting apps. Apple certifies the security of every app it approves for its store (about 250,000 apps), but does acknowledge that some malicious apps can occasionally sneak through.  RIM and Google largely leave users to protect themselves. 

Because smart phones are only a few years old, the art of smart-phone defense is still lagging.  Most people know to use an anti-virus on their computer; smart phone users need a similar software.  Remember, don't click on links in e-mails (on your smart phone or desktop computer) and only go to sites you trust.

How to protect yourself from cell phone hackers (David Sarno - LA Times July 4, 2010)

1.      Familiarize yourself with your phone's security controls.  There are often listed on the phone's options or settings page.  In general, it's recommended that you choose the most restrictive settings.

2.     Read other users' reviews and ratings of apps and buy only those you think you can trust.

3.     Be suspicious if an app asks for access to data that doesn't seem appropriate for its function.  An app for a tick-tack-toe game should not be asking for permission to access your e-mails.

4.     Be wary of text messages or e-mails asking you to click on unfamiliar links even if they appear to be from friends.