Display the default SMS number

China-Hong Kong Card No.2 is a mobile phone card, which can be used between Hong Kong and the Mainland. According to your description, when you are in Hong Kong, sending text messages will default to Hong Kong's mobile phone number, which may be because your current geographical location is Hong Kong.

If you want to use the mainland mobile phone number to send text messages, you can try to enter the full number of the mainland mobile phone number, including the international long-distance area code, when sending text messages. For example, if your mainland mobile phone number is +86 1234567890, you can enter this number when sending SMS instead of just entering the last 10 digits of the mainland mobile phone number.

In addition, you can contact your mobile phone operator for more information about how to use China-Hong Kong One Card No.2 and how to change the default SMS sending number.