Other types of Visual Voicemail: Tap Phone, then Voicemail. iPhone: Select Greeting. Other smartphones: Tap Settings, then Change voicemail greeting. Select Custom, then choose Record. When you're finished recording your greeting, select Stop then Save. Some smartphones may call the voicemail system when you select Change voicemail greeting.
When I go to set up voice mail, it asks me to enter a voicemail code, add a 4 digit number and then it asks to confirm that code, I hit done and it tells me that voicemail is currently unavailable, try later.

It's in the upper right corner of the screen. Now, if you are prompted to type in your password when you are checking voicemail, you should enter the password you just set. When checking voicemail from your iPhone, usually you don't have to type in the password again because your iPhone has automatically sent the password to your carrier already.
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.