The phone hacking scandal at now-defunct tabloid, News of the World, illustrates just how vulnerable phones are to snooping.  Brief and easy-to-guess passwords, along with the cellphone numbers, themselves, contribute mightily to the problem.  

While intercepting voicemail messages is illegal in both the U.S. and the U.K., it can be so "ridiculously easy" as to invite people with unscrupulous motives to do.  It's almost akin to leaving your front door key under the 'Welcome' mat. 

Passwords for Voice- and E-Mail.   Voice-mail passwords can be far easier to crack than email passwords.  While both frequently require the same number of characters - at least 8 - and incorporate lower- and upper-case letters, there are more than 200 trillion possible 8-character passwords for emails, while usually only 10,000 possible combinations for phones.  That's because emails can use the many characters on a keyboard, while phones are limited to the 10 digits on the phone keypad and most U.S. carriers don't require more than a 4-digit PIN - which offers 10,000 combinations.  Finally, people tend to choose passwords that are brief and easy-to-guess. 

One expert says carriers could prevent users from undermining phones' security with "groupthink passwords" and by banning certain common ones - e.g., Vodafone U.K. bars passwords such as 1234 or 4 identical digits.  Other PINs that aren't so transparently vulnerable can still be easily guessed by a hacker - e.g., using the last 4 digits of the phone number, or personal numbers that might be available on Facebook or the Web, such as the user's birth date and month, or high-school graduation year.

For further details, check out [WS Journal, 7/23/11]