You should still get the red dot on the phone icon to show that there's a voicemail. It just won't show the number of voicemails. Just a blank red circle.
That's exactly my point. I don't get the red dot indicating a voicemail.
My guess is that you guys won't get it either if you have iOS 8.1 and perform the following actions. It's very easy to replicate.
1 Go to settings and turn off data.
2. Have someone call you and leave a voice message.
3. Just wait a reasonable amount of time to get the red dot indication of a voicemail in your inbox.
My strong guess is that you won't get that red dot indication. If you have iOS 8.1, then try it out. The only way you'll get to know whether a voicemail is in your inbox is to go to your settings and turn on data. Then visual voicemail will work and you'll get the correct notification.
This is a big problem for those who do not want to turn on data. Simply put, these people will never know they have a voicemail waiting for them unless they 1) suspect a voicemail is waiting for them and check or 2) just happen to call their voicemail to see if a message is there.
Either way, they won't get a voicemail notification - a feature so basic that you can find it in your ordinary dumb phone.
Seriously try it out. Follow the steps and let me know if you can reproduce the problem. That's why I'm asking people who turn off data how they get voicemail notifications when it appears that you can only get it with data on.