You will need to have the following in place to access another voicemail:
The extension number of the voicemail
The pin code for the voicemail (note: if you are accessing a colleagues voicemail whilst they are off, you will need to contact their line manager for permission)
Press the voicemail button, or dial 3000
Press # (note - if you do not do this, it will ask you for your own pin number)
The system will then ask you for the extension number - enter the extension number of the voicemail you wish to access
The system will ask you for the personal identification number - enter the pin number for the extension of the voicemail you wish to access