Forum Discussion

travelaround's avatar
travelaround
Network Novice
Hace 2 años

unable to make and receive phone calls in Mainland China

unable to make and receive phone calls including 611 while traveling in Mainland China, on active t-mobile international pass. anyone has any idea if i can text / email, or online chat with t-mobile ...
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roaming internacional
t-mobile
  • drnewcomb's avatar
    drnewcomb
    Hace 2 años
    travelaround wrote:

    Thanks- simply couldn’t make and receive calls

    So texts and data is working? Does WiFi Calling work? If it does you should get on WiFi and call T-Mobile International Roaming Support at +1-505-998-3793.

    This is why I suggest that international travelers have and know how to use a VoIP backup, like Google Voice, Viber OUT, Skype OUT, FaceTime, etc. .

RoamingAbroad's avatar
RoamingAbroad
Network Novice
Hace 2 años
RoamingAbroad wrote:

I had the same issue while traveling in China: not able to make or receive calls. Data and text still work. Many hours with T-Mobile support did not help. Tried all kinds of things such as reboot the phone, reset network and all settings, call #766# after manually selecting network between China Mobile and China Unicom. Finally figured it out after checking web forums and got some hint from my old working company phone on Verizon without 5G function.
 

The trick is LTE. For the calls to go through, the phone needs to enable VoLTE, and there should be strong LTE signal, and of course roaming needs to be on. If any one of the above conditions is not met, then the call cannot be completed. 
 

The reason for this is that calls may default to 3G but 3G service is being phased out. And if you set to 5G, if will not work b/c T-Mobile's roaming agreement with Chinese carriers do not cover 5G. So if one does not force VoLTE on the phone or LTE signal is absent or weak, calls will not work.

 

Update: played around a bit more and further details are uncovered. I used the iPhone Field Test Mode to determine the signal strength under different conditions/locations (by calling *3001#12345#*) and found out even if the LTE signal is strong around -80 dBm, calls still  cannot go through. The T-Mobile configuration will force the phone to go out of LTE mode when making or receiving a call. Therefore outgoing and incoming calls cannot be completed. This is definitely a T-Mobile problem in China.