Your 4 digit PIN is mainly required to access your voice mail. The Configuration Details sheet supplied with your hardware shows the default PIN given to your phone(s). The PIN must be 4 numerical characters. You can have a different PIN for each phone that you own.
To change your PIN, select: Account – Security – Change Service Pin
From the drop down list, select the phone number for which you wish to change the PIN. Enter your existing PIN in the box marked 'Old Service PIN', and enter your new PIN in the two boxes below that. Then click Save.
If you have forgotten your PIN, click 'Forgot PIN?' This will generate an email to the address associated with the Phone number selected, advising of the current PIN.