No. That's a feature only for providers with mediocre coverage.
ATT, VERIZON the big boys both have mediocre coverage where I am. My life saver is the Wifi Calling when I am home!
Top or best Cellphone company dont mean squat to me, unless it covers where *I* am.
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does wifi calling work on at&t meaning with a nokia lumia on att?
As far as I can tell the "Wi-Fi" calling feature is a OS level implementation that only T-Mobile provides on Androids. I heard that even Windows 8 Phones have that.
ATT offers something calling "FemtoCells" or something like that. But its a separate device you have to buy around $160 and is the size of a router.
What T-Mobile is doing is they already have a great VOIP Backbone and they just enable traffic through WiiFi and is built into the phone.
Advantages are many. Say you are in a well covered area and you enter a building where the signal drops to say one or two bars and you want a strong signal. If you have WiFi you are good to go. The voice is clearer and no static.
When I am home I get 3 bars, but yet I am always on WiFi as I have a 30 Mbps connection and calls are clear!
Someone asked the TMobile CEO about this feature coming to the iPhone and he said iOS does not support that in the present form and I think Apple is trying to push Facetime over this. Catch is, they want everyone to own iPhones!

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there is a tmobile app called bobsled that lets you call people through wifi in any country in the world and any carrier... only avaliable on ios and android
See? there are many apps to do that.. Skype,Tango and so on and on...
What I want is to NOT have to open a separate app. Turn on the feature and use the phone, the dialer and contacts like always. Integration! that's the key.
Plus, when someone calls me on my NUMBER and not the apps, I want to be able to receive the call.