Earlier today Rod wrote about the initial list of Lumia phones that are lined up to receive Windows 10 Mobile when that update is released in December of this year.
While the list is not all inclusive at this point, it contains no third party OEM devices right now, one key element each of those devices have in common is they come with 8GB of internal memory which is a minimum requirement for them as upgrade targets for Windows 10 Mobile.
I have used two of those devices in my regular Windows 10 Mobile testing over the last several months - a Lumia 830 and more recently the Lumia 640.
Initially I was just testing with the 830 but even today, with Windows 10 Mobile build 10586.11, the handset suffers from some lag although it has improved over the last couple of Insider builds.
On the other hand, the Lumia 640, which I picked up from Best Buy several weeks ago for just $60 - a great deal at the time compared to its original retail price of approximately $155 to $177 depending on the cellular band - has handled Windows 10 very well with no lagging issues like the 830.
So today's offer from the Microsoft Store to get the Lumia 640 for $39 (contract free not unlocked) will save you a nice bit of change, $20 of its current retail price of $59.99, plus you have a handset more than capable of running the soon to be released Windows 10 Mobile operating system.
If you are holding off on grabbing the new Lumia 950 series then this handset is the next best thing that will be running Windows 10 Mobile.