I have this issue. When Date+Time is set to automatic it doesn't update at all here in Singapore (Starhub) even though all my other phones work with the same provider (Nokia N9 amongst them). Both the NL920 and NL620 exhibit this behaviour. When I go to Indonesia it does update automatically with INDOSAT, which is good. But then coming back to Singapore it's wrong again so I have to do it manually.
Very strange that this would not "just work".
I can confirm that the problem in Australia is Vodafone.
The phone is an unlocked Lumia 920 and was fine with Telstra. On Vodafone no automatic Date + Time.
Pretty ordinary experience
Adam
Adam Cogan's Blog ? Microsoft Regional Director, SSW Chief Architect, MVP, Scrum Master, Speaker
It work sometimes on my Lumia 920.