(01)-4407400 - Common access dial in number (let's you call a freespeech 'extension'  from landline or mobile)

1742 - Echo Test.

1743 - Will tell you your number

1744 - Will dial your own Missed Call Handler (Voicemail / Forwarding) - Usefull if you want to check the setup or test annoucements.
TIP: If you want a greeting message for voicemail this is a perfect way to get a recording suitable for upload.