To check if Optus VoiceMail is set up on your mobile phone dial 321. If you get the message Ding Dong that number is not listed your VoiceMail is not activated.If you would like to activate or deactivate Optus VoiceMail, please free call 1504, from your mobile phone.This service is available 24x7 and will confirm your status via SMS.ser Options with Optus Voicemail. With 321 (Optus-mobile) VoiceMail, you can get help with your VoiceMail options at any time by dialling 0. Step 1 Access VoiceMail by dialling 321. Step 2 At any time Press 0 to listen to detailed information on your options such as changing your VoiceMail greeting.