It's rumoured to be a 'big bang' this time - on 14th March. The only exception is if you are on 300K, in which case you might want to stay on that with the 30GB cap rather than going to 1MB with the 5GB cap (or is it 3GB - I've lost track), or if you are on 750KB and are getting BB through a PACE STB, in which case you'll need an upgrade to a Samsung STB. In either of these cases, you'll have to ring CS to arrange an upgrade.
Still no 'official' announcement though.