To check your voicemail on a PBX as a Service handset, please dial *123 and enter your PIN when prompted. Once logged in, simply follow the voice prompts. Should you need to retrieve your extension's PIN number, please see the following: Checking / Changing an Extension's PIN
If you are accessing a global or other user's mailbox, dial *124, then when prompted enter the mailbox number and PIN. Once logged in, simply follow the voice prompts.
If you are having issues dialling voicemail from a Cisco handset, where it only lets you dial the first 2 digits, please follow this guide to reconfigure your phone's dial plan: Issues dialling voicemail from Cisco phones