I currently have the Lumia 810. Yes it's old but I like it and works great with Preview for Developers upgrade. However, it's getting slow and my wife and I would like a better camera for nature walks and trips. I can't afford a flagship Windows Phone so I'm considering an unlocked Lumia 830 since it has a Pureview camera. I'm on T-Mobile in the U.S. and would like some suggestions and thoughts regarding the quality of the camera, using it on T-Mobile, and does it support WiFi Calling? I have also thought about the 640 XL but it doesn't have Pureview. Hope in the near future someone can post pictures comparing the two cameras. Thank you in advance.