Last year's Lumia 635 was a reasonable seller for Microsoft. Not quite as successful globally as the 53x, but Microsoft's biggest seller stateside.
Now the company has replaced it with two handsets- the 640 and 640 XL (although the latter is more of a replacement for the giant 1320) and promised that these two phones will be amongst the bistro get Windows 10 Mobile when it arrives.
The 640 has a better (IPS and 720p) screen than its predecessor as well as gaining a front-facing 1MP camera on the front and bumping the rear camera to 8MP and adding a flash.
For a phone that's going to sell for well under £100 once the box-shifters get hold of it, that's a pretty impressive set of specs.