@jpdl when did you purchase your phone? originally this was a firm ware update but that was awhile ago, i got my phone 3 weeks ago and in came right on the phone. at this price i doubt you can find one over a month old so all new ones should have the update
This phone DOES come with Wifi Calling out of the box and it works great by the way.
You can call, receive calls and send/receive SMSs via Wifi, and yes, it does use your minutes.
Sorry but the other answer is not correct.
-First, this phone does not currently have the wifi calling feature, it *may* be added by t-mobile later in a firmware update
-Second, if the feature is added, prepaid users will ALWAYS be deducted minutes, even if you're using wifi calling. Post-paid users may or may not be deducted minutes, depending on their plan and features.
No, Wi-Fi calling does not use minutes. If you have a Wi-Fi network and set the Wi-Fi calling to preferred, it'll not use your minutes.