Generally, these greetings should be brief for an individual. State your name and a query for the caller's information. You can also include a backup number for people to reach you if you like. For an organization, it's a good idea to announce your standard office hours. Dial *98 on your OnSIP-registered phone. Enter your voicemail box number. Enter the PIN/password for your voicemail box. Press 0 for voicemail box options. Press 1 for unavailable greeting.
On the Greeting page there are two options. The standard option is to use the default iPhone voicemail message, but you can also record a custom message. If you already have a custom iPhone voicemail message recorded, tap Play to listen to it now. Otherwise tap Custom.

“Hello! You’ve reached the voicemail of [your name], [your job title]. I’m currently either away from my desk or on the other line. Please leave your name, telephone number, and a short message after the beep, and I’ll be sure to get back to you as soon as I’m available.” Press and hold the 1 key to access the voicemail system. When you hear the recorded message, press the # key to bring you to the system menu. Press 4, for the Personal Options followed by 2 for Personal Greeting. Follow the prompts to record, listen to, re-record and save your greeting. How do I change my voicemail number on Samsung Galaxy s8? Find “Voicemail number” Press Phone. Press the menu icon. Press Settings. Press Voicemail settings. Press Voicemail number. Save voicemail number. Key in +61414121121 and press OK. +61414121121. Return to the home screen. Press the Home key to return to the home screen. Dial voicemail: Press and then hold on the envelope icon displayed on the main screen. Enter Your Accounts Password: Enter the password if prompted. Delete voicemail: Tap 7 on any voicemail and it will be deleted successfully. Open the dial pad on the device. Open the application drawer and scroll through to find the Phone app. Dial Voicemail. Tapping the number 1 and then hitting the green phone icon at the bottom should call Voicemail. Enter a password (if there is one). Skip through messages. Delete a voicemail. Log into Google Voice. Click on the gear icon. Select “Settings” from the menu options. Click the “Voicemail & Text” button. Click “Record New Greeting” in the Voicemail Greeting section. Enter the name for the greeting you are going to record. Select forwarding phones. Click “Connect.”
If voice mail options are grayed out, you're using the Skype for Business voice mail service with cloud PSTN. Voice mail options aren't available in Outlook.