Says Murtazin (via Soft):
Nokia R&D - 4 Windows Phone 7 and 1 tablet (Win8 presumably). 2 phones used chassis 1, 2 based on chassis 2 - like HTC Ignate (middle end).
Perhaps the most notable piece of the tweet is the speculation that Nokia is working on a Windows 8 tablet.
Chassis 1 devices will likely run on 1GHz processors, have 8GB internal storage and a 5MP camera. Chassis 2 devices will be lower-end, running on 800MHz processors, like the HTC Ignite.
It is still unclear when the first Nokia WP7 devices will hit the market, and at what price.