Unicom, one card two, how can Hong Kong send and receive short messages in Shenzhen?

After the opening of Unicom Hong Kong's one-card dual-number service, there are two numbers in a SIM card. In addition to Unicom's mobile phone number, there is also the number of a Hong Kong cooperative operator. As long as you roam in the cooperative operator's network (you don't need to choose in Chinese mainland), you can use it directly in Hong Kong and Chinese mainland without switching networks.

Note: When using this service, the number of SMS center must be changed to +86 13090548805. If the user returns to Chinese mainland, there is no need to change it back. However, if the service of one card and two numbers is cancelled, the number of the SMS center must be changed to the number of the local Unicom.