The whole reason behind T-Mobile and Wi-Fi calling was to get rid of my land line. Well I have been holding back and it may be a good thing because of something I have noticed. For me Wi-Fi calling only connects when I turn on the phone and unlock the screen. If I am out of range of Wi-Fi and then return to a hot spot Wi-Fi calling will not connect until I turn on and unlock the screen. How long in the hotspot does not matter. My son-in-law called and it didn't go through so he called on my landline. I checked my 521 and it said no service "I have poor coverage at my house". The Wi-Fi calling square was blue and while I watched it turned green and my coverage said Wi-Fi calling. I will have to call customer service................calfee