Slydial is an app that is available for both iOS and Android. Free accounts are available but they require you to listen to an ad before making your call.
Navigate to your Phone app located at the bottom of your iPhone home screen. Tap-open the Phone app. Once you have done that, you will see a voicemail logo the bottom right corner of the window that has opened, select that voicemail icon. That action will open the visual voicemail interface. At first, all you will see is a blank screen with a

An excellent business voicemail greeting conveys your level of professionalism and competence while also providing your callers with a glimpse into your company’s culture and level of care. As minor as it may seem, your voicemail greeting can instill confidence and trust in your callers or it can be a cause for concern.
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.