My wife uses an iphone4, on 2Degrees and when somebody calls and leaves a voice mail message, she gets notified of the missed call, but despite having all the settings required setup in her iphone, she doesn't receive any separate voicemail message notification (she was on Vodafone a month earlier and didn't have this issue)

Also, I know 2 other iphone users (1 x iphone4, and 1 x iphone3) who have also recently changed from Vodafone to 2Degrees, and now they don't receive voicemail received notifications either (whereas on Vodafone they did)

Does anyone know of an easy fix? Is there a dial-in code that enables this feature?
Surely it can't be that complex? 

Needing help please as this is very frustrating and costly having to dial into the voicemail number after each call to see if any messages were actually left