How to send messages from the mainland to Hong Kong, Hong Kong also uses mainland cards. How to send?

Under normal circumstances, the method of sending the mainland mobile phone number to the local mobile phone number in Hong Kong is "+852 XXXXXXXX" (where xxxxxxxx stands for the 8-digit mobile phone number in Hong Kong) or "00852XXXXXXXX" without spaces in the middle. This method is feasible. I used the People's Card in Hongkong and received short messages from friends of China Mobile and China Unicom.

Well, if a mainland card roams to Hong Kong, if someone wants to send a message to this card in China, there is no need to do anything special, just treat this card as if it is in China, just like sending a text message at ordinary times. Note that the premise is that this mainland card can still have a signal when roaming to Hong Kong. I tried to move through the M-Zone, and there was no signal at all (international roaming was not enabled), but a friend's card was Unicom. After arriving in Hong Kong, she still sent and received text messages and made phone calls normally.