The news of the moment in the UK is the News of the World Phone Hacking Scandal. With rumours that there are lists of 1000’s of celebrities, Government officials, criminals and victims who have had their phones hacked by journalists of the news of the world hysteria has hit the british press and the newspaper buckled under pressure and shut down.
Baffled by the reaction, I thought about the story, and suspect there is a fair amount of misunderstanding amongst the public. Especially when it comes to the question “What is Phone Hacking”. And the first thing to remember it is nothing like the underworld of computer hacking, virus writing, web page hijacking, or even phreaking to make free phone calls. No, what it is is simply playing off human lazyness and taking advantage of a functionality mobile phone networks introduced many years ago.
Almost every phone operator gives the option to check your mobile phone messages “remotely” ie from another phone when you do not have it with you. This is also the case for most modern answerphones for landlines.

For those who have not been following the stories, have a look on google news

For mobile phones it is simple:
1) You phone your mobile phone
2) Wait for the voicemail divert
3) Press the * key
4) Enter your PIN code

And your messages are read out as if you were accessing it from your own mobile phone.
The vast majority of users are (or until now) were unaware of this as they had no use for it and therefore would never go into their settings to change the PIN code.
Therefore, for most people the default will work – and this includes celebrities.
Clearly, you can’t initiate this plan if the person you are trying to get hold of answers the phone, so the ususal plan is to work in pairs where one person phones and if the person picks up the 2nd person immediately phones from another line and will immediately get through to voicemail. Meanwhile the original person phoning who got through to the person will give some excuse such as claim to be a sales person offering products that will be refused or that they have dialed an incorrect number opening the way for the other person who has got into the voicemail to listen through the messages saved, find out any numbers left by people who have left messages or even delete messages.

This BBC news site story has more info.
The guardian has a whole section of their website dedicated to it.

Out of curiosity I decided to try and hack my own phone having done a bit of googling to find the default pin codes.
The first problem i found was that I had actually disabled my voicemail which would explain why I hadn’t had any messages recently – not that i use it much. Next, having enabled it after 10 seconds of ringing I got through, followed the process only to find the default pins did not work, suggesting i had in fact changed the pin code at some point and have no idea what it is so good luck phone hackers getting into my voicemail!!