O2 sent me a Windows Phone 7
They sent me one back in the day to test.
Huge slab of a device.
Now the OS itself felt unfinished in many ways but was fairly intuitive.
But one of the things that I feel definitely helped it to an early grave was the decision by MS to release version 8 (I think it was - it might've been a 7.x - it was some time ago) but not have it compatible with the earlier hardware.
So anyone who'd bought into their platform was screwed over and why stick with a manufacturer that throws their devices under the bus one version later? Not even Samsung do that.