It's called Uncuva, and it's supported by WHSmith's old ebookstore partner, Mobcast. It's sharing the same servers as Mobcast's other partners, including Orange, T-Mobile, Vodafone and Singapore Telecom.(Mobcast runs their ebookstores.)
Is it just me, or does that name sound like an infectious disease?
Snide comments aside, Uncuva launched earlier this month. Mobcast will be supporting this ebookstore in the UK market, and they have already releasedthat works with it. An iOS pp is in the works, too. This ebookstore will offer the same selection that WHSmith used to have, and all ebooks that had been bought via WHSmith before the changeover should still be in your account.