Who is your carrier?
Years ago carriers did indeed charge for Visual Voice Mail, but I am not aware of any that still do so.
If you ever had an early generation cell phone, you would know that, to access your voicemail, you had to actually call your own number and then go through a series of prompts to listen to, save, delete, or forward your messages. All of this wasted time and, with most carriers, actually ate into your monthly "minutes" available.
So, along came Visual Voice Mail which stores the messages directly on your phone, allows you to scroll through a list and listen to them in any order or summarily delete them without bothering to listen to your annoying aunt asking, for the umpteenth time, when you are going to pay her a visit.
It's a lot better than the old alternative and should be free...