Visual Voicemail is an iPhone feature that provides visual access to voicemail content. It enables you to select the message you want to listen to, without going through all of your voicemail messages.
Unfortunately, preventing spam callers from leaving a voicemail on your cell phone can be tricky. We've researched the options from each carrier and tested a number of call blocking apps to see

If Set Up Now doesn’t appear, then that means your phone has been set to the automated voicemail option. You can change it whenever you like, though. All you have to do is tap Greeting, which should be at the top-left of the screen.Tap Record, and then speak slowly and clearly into the phone so that your message is recorded.When you are finished, hit Stop.
Voicemails have been around in one form or another since the beginning telephone communications. This feature still manages to make its way on every smartphone, despite the rate in which technology is evolving. The reason for this is usefulness – you won’t miss any unanswered calls even if your phone is off. The voice messages from your callers will be transferred to your voicemail box and you’ll be able to listen to them at a later date.