I had a fortunate accident that landed me not only a lumia 640 from tmobiles website, but also a prepaid version from Walmart. Now I used the prepaid version first and my postpaid one arrived yesterday. In the software, specifically pertaining to the navbar and touch functions, on the prepaid one there is an arrow on the far left of the navbar which is how you hide the navbar and you have double tap to wake but no double tap to wake but no double tap to shut the screen off. On my postpaid version, like the international you swipe up from the bottom to hide or show the navbar, there is no arrow on the left, and you can double tap the navbar to shut the screen off. Otherwise both function identically wifi calling and volte working fine on both. Checked for updates on both and both appear to be up to date.