Why can I receive short messages without installing a sim card on my smartphone in Redmi?

Red rice phone

If you use miui system, you will have a Xiaomi account. If you have bound your mobile phone number before, Xiaomi account is equivalent to your mobile phone number, if there is a network. Users who use MIUI system will send short messages to your mobile phone number when there is a network, and send them to your mobile phone through Xiaomi account. This function is called free SMS, which can only be used between MIUI.

Hope to adopt