You can change the global voicemail greetings for all the extension users or change voicemail greeting for a specific extension. A quick start guide for the administrator who is new to Yeastar S-Series VoIP PBX.
Start your phone up and launch the Phone app. Turn on your phone and tap the Phone app. ...Access your additional phone options. In the top-right corner of the screen, tap the More Options button (the three vertical dots), and then tap Settings.Choose to adjust your call settings. Next, tap Calls in the menu that appears.

If you’ve already created a custom voicemail on your iPhone, you can tap Play to see how your voicemail sounds. If you’re interested in creating a new message, tap the Custom button. From here, you can start recording your message by tapping Record and tapping Stop whenever you’re finished. Once you’re finished recording, tap on Play to make sure the message comes across as you’d like and hit Save (in the upper right) to save it as your voicemail.
Just NowCall your iPhone from another phone and try to leave yourself a voicemail. Go to the keypad and press and hold on the 1, or press the Call Voicemail button. This dials voicemail. Check if you have any missed messages. On the Voicemail screen, tap Greeting. Then change your greeting to either custom or default.