Sorry to hear this is giving you trouble, especially while you're abroad.
If its worked for you at your home, I assume you're already familiar with the basics.
Some other things to check, do you have at least 2 bars of signal with this wifi network? Can your phone browse via this wifi network?
If so, try this:
- From the Home screen, tap Settings.
- Tap Applications.
- Tap Manage Applications.
- Tap All.
- Find the Wi-Fi calling application.
- Tap Clear Data.
Then shut WiFi Calling off for 1 min, then turn it back on and once the icon's is blue again, retry.
Some other things to keep in mind: If the ISP has web re-direction turned on, WiFi calling can't work. If the WiFi network has MAC filtering, ensure your device's MAC address is listed.
Using WiFi calling through an international network creates a large number of factors that could be at play here. If the above information has not solved your problem, please contact us directly when you can, you can use online chat here or call our international tech support number here: +1-505-998-3793. (if calling from a non - US landline, use the ILD code in place of the "+")
I am now in Australia (Brisbane area) and *Clear Data* seemed to do the trick!
Wi-Fi calling is now enabled and I was just able to check messages successfully!
I don't want to try calling anyone since it's now about 3:15am in California, but as the locals say, I'll give it a go tomorrow morning.
When I first arrived in Australia I tried again with the same bad result ("Wi_Fi Connection Error W006.15 or T-Mibile Network Error") so I was discouraged. But after the Clear Data maneuver I briefly received a W006.25 error (not 6.15), but then the app apparently retried and Enabled.
Summary: I was never able to get Wi-Fi calling to work anywhere in New Zealand. After tmo_chris' suggestion that I execute 'Clear Data' in the Wi-Fi calling application on the phoneI was able to occasionally connect in Australia. This is generalizing, but it seemed that if a Wi-Fi access point required going to the phone's browser and signing a waver (McDonalds and etc), then Wi-Fi calling would not work even if the phone's browser and email and other apps worked fine with the Internet. If the access point did NOT require any sign-in (apart from perhaps entering the network key) then Wi-Fi calling would work fine.
For Wi-Fi calling to be more useful when traveling this limitation needs to be worked out.