The new UK Kindle edition of A Game of Thrones was released on Christmas Eve, but the remaining books are still unavailable on Amazon. However, Voyager have revealed today that the new edition of A Clash of Kings will be released on 3 February, with A Storm of Swords to follow by the end of the month and A Feast for Crows by the end of March. As with the new version of A Game of Thrones, these new editions have been proof-read and formatted properly, hopefully avoiding the problems found in the existing versions. And yes, the ebook of A Storm of Swords will be in one volume (the UK paperback is in two). Voyager also plan to release the ebook of A Dance with Dragons simultaneously with the hardcover, barring unforeseen events.
It is unclear when or if these new UK Kindle editions will be replicated for the American market.
In additional news, Voyager have said they have no plans to change the British ASoIaF covers. The American covers will be changing to new versions in March (to the British ones, although the British ADWD cover is now on AGoT and presumably vice versa, which could get confusing).