With this method, you don’t need a third-party app. Call the person you want to chat with, then tap the “Add Call” button on your phone’s screen. Dial your own phone number—the one you’re calling from. This will take you to your voicemail. Once your voicemail has started recording, tap the “Merge Calls” button on your screen. Now, you’ll record your phone conversation onto a voicemail message. When you’re done with the call, you can tap the share button to export it to your Mac via Airdrop, to the Voice Memos app, or transfer it via email or text message. The file is recorded as an M4A, so depending on what you want to do with it, you may need to convert it to MP3 before uploading it to other apps.
By default, the telephone number is the one assigned to you by your organization, but it could also be a cell phone number or email address. In that case, voice mail would be played back through your email Inbox.

Hello, you have reached the dental office of Dr. X. We are busy assisting a patient now, but will call you back as soon as possible. Please leave your name, reason for calling, and your number. If this is an urgent enquiry, please call 911. In this case, the dentist is giving a reason for not being available and they’re providing a way to prioritize the patients who need the most help. They’re also leaving an emergency number for the most severe of situations.
To enable Visual Voicemail, you must create a password by accessing your voicemail and then record a greeting as follows: Access the Telephone app, select the Voicemail tab and tap Configure now. Select a password for your voicemail and tap Done. Confirm your password by re-entering it and tap Done. Select Custom if you wish to save a new greeting or Default if you don’t wish to edit your message. Tap Save.