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I'm currently on T-Mobile US iPhone 6s...mine is just stucked on waiting for activation.

Not with wifi calling, but after changing my SIM card, I cannot activate iMessage or FaceTime on my iPhone 6s Plus on AT&T. Running iOS 10.0b2.
 
I downgraded back to iOS 9 and my wifi calling started working again.

Yeah stupid move on my part. I don't have access to computers with iTunes so I'm pretty much screwed. My fault for downloading a beta on my main device.
 
I've got an iPhone 6 on iOS 10 public beta and at first my T-Mobile Wifi did not work but after I turned it off and back on in settings and shutdown / restart it kicked back on. Try that and see if the works.
 
I've got an iPhone 6 on iOS 10 public beta and at first my T-Mobile Wifi did not work but after I turned it off and back on in settings and shutdown / restart it kicked back on. Try that and see if the works.

I actually got it to work after when I installed iOS 10 the second time.
 
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