Not come across a Dual SIM Windows Phone before (but guess I wasn't really looking so don't shoot me).
This got announced today in the UK - of note is that it is Archos first Windows Phone
"The ARCHOS 40 Cesium features two sim card slots, letting you mix personal and work together on the same smartphone. This is made even easier with Windows Phone's People, Family and Groups system bringing together your social feeds, emails, texts and calls together into groups of contacts. Transferring these contacts from your existing smartphone is easy too with specialized wizards to help you transfer from Android or iOS."
(And am I correct in thinking that this is the model currently favoured by Lord Monckton?)