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.
— Steve Hemmerstoffer (@stagueve) May 28, 2015
Of course 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, but given the limited information so far I think we can leave the speculation at this point. Presumably we will be seeing much more soon over the next hours and days.