A tip from a reader brought me to this article on Telstra in Australia saying that they intend to upgrade their 3.5G network in Australia first to 21 MBit/s in 2009 and later on to 42 MBit/s. The step to 21 MBit/s seems logical. According to the 3GPP standards, that's an upgrade to 64QAM modulation. If they have the latest base stations from Ericsson, they might be able to do this without a hardware upgrade.
Concerning the 42 MBit/s, that sounds like the 28 MBit/s one gets with MIMO plus 64QAM modulation on top. When I last had a look at the standards document referenced above, there was not yet a terminal class for this maximum speed.
A note of caution: Such speeds can only be reached under very special circumstances, i.e. no other subscribers in the cell and the base station antenna very close by.