IOS 8: T-Mobile WiFi Calling on 5s issues

Question

Is anyone out there having problems with WiFi calling w/ their iPhone on T-Mobile?
I updated my Wife's 5s to iOS 8, and enabled the feature in settings because we suffer from terrible calling performance on T-Mobile (1 maybe 2 bars of signal) in our home. She still drops calls regularly. I dropped a call three times while speaking with T-Mo support about it last night.
They told me that they had to provision the feature on the account, which they did a couple of days ago, but even after doing so, it still doesn't seem to be working. How can I tell if the iPhone is using WiFi on a call? Is there an option to force it to use WiFi for calls?
I have an (older, rectangle 2nd gen) Time Capsule in bridge mode that serves WiFi to the house, but I don't think it is the issue because other wireless devices work just fine and I have no other WiFi issues. Also, the other phones on our T-Mobile account are all Android phones that support WiFi calling and they all seem to be working flawlessly with WiFi calling and indicate when the phone is placing the call over WiFi.
So, aside from using a different WiFi base station (such as T-Mobile's new WiFi router - which I won't do unless it supports bridge mode because I have a much more robust Cisco firewall doing the routing) I can only conclude this is an Apple/T-Mobile issue with their implementation of WiFi calling.
Just wondered what other iOS 8 & T-Mobile users were seeing with WiFi calling.
Thanks in advance, any helpful info would be appreciated.
-Rob

Answer 1

@chattphotos: I didn't try pingtest, but with all due respect, I don't see the point. A connection with a 10ms ping and 100 down and 4 up should PLENTY!
@Hofstrajet: My wife's phone shows the same as the screenshot you posted. It definitely says T-Mobile Wifi
@Prelude_007 When you say you can connect at home, does that mean you can somehow make WiFi calls there? How do you know the call is actually going over WiFi from home and not Cellular? What is your cell signal like at home? At your work, it might not work because they probably are more restrictive with what kinds of traffic they will allow. It could be that your IT staff have firewall rules preventing anything but web and email traffic to pass. I am sure this VoIP protocol uses some different ports, but I haven't seen the details on how it was implemented yet.
My thoughts at this moment is that either there is an issue in iOS that may or may not be limited to the 5s, or that T-Mobile still needs to do something on their end.
The only thing I have left to try on my end is a different WiFi access point. but given that my Samsung Note 3, my son's Note 3, and another Galaxy S5 all have NO PROBLEMS making/taking WiFi calls, it has to be an Apple <-> T-Mobile issue.