When you're in a call, wait for the Add Call button to light up, so you can add a third caller via 3-way calling. Tell the other person to wait, click the button, and call yourself. Stay on the line and listen to your own voice mail greeting, then for the tone that indicates recording has begun. Tap Merge Calls. All three calls are merged—and the third one (your voice mail) is taping the other two.
Call someone back by using the call controls under the contact details at the top.

With Visual Voicemail, you can see a list of your messages and choose which ones to listen to or delete. Learn how to set up and transfer your existing voicemail. Create a voicemail password, then tap Done. Enter your password again to confirm it, then tap Done. Select Custom or Default. If you choose Custom, you can record a new greeting. Go to the Phone app, then tap the Voicemail tab. Tap Set Up Now. Enter your password,* then tap done. Record a custom greeting or use the default greeting, then tap Save.
The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.