French site Nowehereelse.fr regularly get their hands on early Windows Phone prototype parts, and have just tweeted this picture of a curved screen windows phone handset which is presumably an upcoming device.
something which does cause some doubt on whether this is a new device is the fact that it says proto.nokia.com but then devices tend to have rather long lead times, and this may date from before the rebrand.
WindowsBlogItalia speculates that this may be the Talkman Rounded edges, 5.2-inch qHD display with physical buttons – Talkman – the second high-end Lumia coming with Windows Mobile 10