Windows Central posted a video comparison between the Microsoft Lumia 640 and Lumia 635
The Lumia 635 is a smaller device with a 4.5-inch 480p display while the Lumia 640 improves on that with a 5-inch 720p HD display. The Lumia 640 also features Glance screen, which lets you see the time and other lock screen content when your phone is on standby. That's missing on the Lumia 635.Microsoft Lumia 640 vs Lumia 635 video comparison
Because of the bigger display on the Lumia 640, it's also bigger overall compared to the Lumia 635. The Lumia 640 is wider and taller than the Lumia 635, but the 640 is a little thinner.
It's also worth noting that the Lumia 635 does not have a front-facing camera. There's one on the Lumia 640, and it's one megapixel for your selfies. There's a 5-megapixel camera on the back of the Lumia 635, but there's no flash. The Lumia 640 improves on that with 8 megapixels and an LED flash.
