What card does Korea use to receive short messages?

China Unicom international roaming unified customer service telephone number 8618618610010. Only the mobile users of China Unicom can use it in the international roaming state, and the dialing method is the same as that of ordinary domestic mobile phone numbers.

It's free for users to call this number through Unicom's mobile phone outside China, but it's not free to call18618610010 through contact methods other than China Unicom.