When your phone only rings once then cuts out, this fault is known as "ring trip". It can be caused by a number of things either inside or outside your property, and will require a process of elimination to track down the cause of the fault.
Setting up visual voicemail on an iPhone is straightforward. First, check if your carrier allows for visual voicemail; many major providers do.

Open your Voicemail app.Tap, or tap and hold the message you want to save.In the menu that appears, tap the one that says “save”, “export” or “archive.”Select the storage location in your phone you would like the message to go to, and tap “OK” or “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.