Not having all the details I can't provide a definite root cause analysis. I can suggest it could be to do with a back of house change on the accounts in question rather than any technical change.
Sorry, I didn't mean to high jack this thread, but now you've got my interest.
Exactly how can a back of house change on our accounts effect our mobile coverage if there's no difference on the tower for which phone gets connection?
I know our guys in all states are having similar issues.
But for me personally my mobile phone sits in a cradle on my window sill and I use a Bluetooth headset for all calls.
I never move my phone, it has been in the same place and had reasonable reception right up to the day we changed our contracts. Now I get on average 6-8 incoming calls per day that go straight to voicemail. Plus several outgoing bad connections and/or dropouts.
The explanation I heard that we had been a premium customer, but have now been moved down made sense.
But if you're saying that no one gets preference in the towers, I'm wondering how an administration error in the back office can effect my mobile coverage.
Or we can just move on from this mobile discussion and admit that Telstra have throttled down their internet speeds in some areas to push customers over to NBN.