* Press the star key
* Try commonly used passwords: 0000, 1234, 4321, 5214, or 502915
* This should allow you to change the password and even the greetings on the phone.
This process only works if you know the person has a digital voicemail. If you know the person you can try to guess their password. Often the password is something that has meaning to the person. Most voicemail codes are four numbers.
It is illegal to break into voicemail if you are not the owner of that voicemail box. Like snail mail, there are privacy laws. Many individuals who seek to break a code for voicemail have either lost their code or want to play a prank on their friends. There are also those who would change voicemail for other means.
You should not hack into another's phone. If caught there can be serious consequences, especially because most countries like the US and UK are cracking down on misuse of mobile phones in order to protect citizens.
The above steps should only be used on your own phone if you have forgotten your phone code. You will also note though, that you can call your service provider and ask them to help you reset your voicemail password should you have forgotten it. They will not be able to tell you the old one, but the steps to go about changing it.
Most mobile phone service providers ask for a special security phrase that tells them you are on the account and able to access account information. Therefore, the service member should be able to walk you through the process if you give them that code. They can provide helpful hints to the code, but they cannot give out the code either.