An extension is a short internal number. Extensions allow users to make and receive calls. You can assign extensions to every employee in your organization.
Or maybe you just haven't updated your voicemail greeting. Let's look at how to change and record voicemail greetings on iPhone. Step 1: Access to Voicemail from Phone. When you set up Voicemail for iPhone 7, you can enter the Phone app, and then tap on "Voicemail" to access to Voicemail to change for the desired information.

From another Ooma Office phone. Dial your internal extension number and wait for the call to roll to voicemail. Press [*] and enter your PIN. Select option 5 from the main voicemail menu. Select option 1 from the submenu to record a new greeting, or option 2 from the submenu to record a new name.
If your carrier supports the iPhone voicemail feature, you can retrieve and listen to your voicemail right from within the “Phone” app and call your contacts back by simply tapping their messages. That type of functionality is pretty neat and useful, because it saves you actual time. If not supported by your carrier, you will not be able to see the visual overview of your voicemail inbox and use any of the related features. Tapping the “Voicemail” tab in your “Phone” app will simply call the number associated with your voicemail box. So let’s get going with creating our custom voicemail greeting on iPhone! How to record your own Voicemail on iPhone Phone → Voicemail → Greeting → Custom → Record → Save