My mobile phone is Xiaomi. I am in Vietnam now, using a Vietnamese card. I can call. Why can't you send text messages?

The number of SMS service centers is different, and the number of SMS service centers of each operator is also different. The domestic service number starts with +86. If you don't modify it, you will use the network of foreign operators when you go abroad, so the short message will be released. Android phone, open the SMS icon, find the settings button, generally there is a "SMS center", modify it. Each model is different. If you can't find a friend of the same model, still consult on the forum.