phone håcking - what does it really mean?

I've heard and read some stuff so I don't know what all happened as far as what "physically" happened with supposed voicemail "hacking" that happened in Great Britain. Some of what I've heard is that those involved in the hacking just applied default access codes noting that many people are careless about their voicemail and never changed the default code e.g. for T-Mobile the default voicemail passcode is the last four digits of your phone number.

I've also heard that this "hacking" can be accomplished by a non-secured voicemail box so that when you access voicemail from the phone you can choose to not require a passcode when accessing it. Not requiring the passcode means that someone could "spoof" caller ID to make it the same as your phone number and pose as the owner of the number and thus access the voicemail box.

Has anyone heard of what I've written above and does anyone know anything more than what I've heard?

Note: In reading my RSS feed I came across most of the answers to my query:

http://gizmodo.com/5822574/how-news-of-the-world-hacked-everybodys-phones

Turns out it's a bunch of stuff about caller ID spoofing and not changing default access codes that leaves a number vulnerable.

 

I just like using the option key