Why is my voicemail taking so long to set up?

I was wondering why I never get voicemails and then I look and I haven't set up a voicemail yet and when I press set up voicemail it asked if I want a default or custom voicemail and I pick default and it says setting up voicemail but it never actually sets up and then it goes back to the set up voicemail as an option again. And I have an iPhone 5 iOS 7 why is it taking so long?

Can I have more info on this?