The next day, I open up the package. The unboxing video needs editing, so that will come soon. But here are some pictures of it and it in comparison to the Nokia Lumia 520.
(Note that the 640 has Windows 10 Mobile while the 520 has WP 8.1)
Here are the start screens. Note that the 640 has on-screen navigation buttons.
Here are the back plates. The 520 is smaller, and it has more curvy edges. They unfortunately both have the ugly AT&T logo because they are both GoPhones.
These are the lock screens, as well as more size comparison.
Like I already said, the 520 has curvier edges.
Here's a comparison of Cortana on Windows 10 Mobile and Windows Phone 8.1.
Here's the lovely Microsoft Logo on the back. :)