Did they say that this morning?
Hopefully someone will provide a hack for this (just for O2 SIMs, obviously)...
They didn't say anything about what would work with hacks this morning! As far as they were concerned, hacking it isn't an option!
But on the net, it's widely known that unlocking and popping your own SIM in activates everything except the visual voicemail. Also, a hack to provide it is pretty much impossible as the voicemail is held on your networks server and without access to that, there's no way to provide the individual message's origins etc, which is what the visual voicemail does.