My exchange (Devizes) met it's trigger point a few days ago. It should get a build date of around the end of april/beginning of march, if the other triggered exchanges are anything to go by. ADSLGuide.org.uk say that once the exchange has a build date then you can go ahead and place a pre-order - it list Plusnet as one of the ISPs that can place pre-orders.
Now, I am thinking of pre-ordering soon to take advantage of the free activation deal on offer at the moment. Can PlusNet confirm that this is a possibility? If it isn't then I may go and pre-order with Nildram or Pipex who offer similar deals i believe.
Does free activation end in march? If so, will it cover a pre-order for an exchange due to go live in may even if the order is placed in february?