iPhone4S + IOS 6 + Verizon
I had the same problems as you had today. After a vendor tried to call me - I heard the beep, no notification, never went to vm - never knew who it was. This is what I did
1. I killed all the apps
2. I shut down the phone and restarted
3. Tested (2 times with different numbers) the call wait and it worked as it used to be before the IOS 6 upgrade.
I also manually never did restart after the upgrade was done. This may be a solution for others.
as far as i can tell, the notification settings aren't for missed calls. If i miss a call then there is no direct notification (Banner or Alert (dialog box)). All i get is a message on lockscreen, a message in
Notification Center and the red icon on the app. But i never got a Banner or Alert for anything related with the telephone app.
I do get Alerts or Banners for new voice messages. But these notifications stem from the message app.
I really want to know what these notification settings are intended for. Maybe someone provide a screenshot of an Alert or Banner notification from his telephone app…