To set up Visual Voicemail, tap Set Up Now. You’ll be prompted to enter and confirm a voicemail password. Next, you’ll have the option to choose the default voicemail greeting or record your own. If you want to record your own custom greeting, tap Custom. Once you’ve entered created your password and chosen your greeting, you’ll be able to receive voicemails and view them in the Phone app.
Visual Voicemail is a feature on iPhones that allows iOS to transcribe the voicemails people leave for you. This way you can read the voicemail like a text message instead of having to listen to it.

Tripboba.com - Voicemail is a voice message that a caller will leave to your mailbox when you’re absent or busy with another conversation. The same goes if you’re trying to call someone else and they don’t answer. You can leave a voice message and they will receive the mail, allowing them to hear what you want to say.
If you are recording a voicemail message for business, be sure you include your name and your company's name, so people know who they are calling and were they are reaching them. If you do not include the business name, they may think they have mistakenly called you at your personal number. You will also want to make sure to give callers the option to speak to someone who is currently available, an operator or other representative, by pressing a certain key (check with IT personnel to see what this might be).