Mainland cards cannot be used directly in Hong Kong, and mobile phones using mainland cards in Hong Kong belong to international roaming. There are two solutions: you can buy Hong Kong calling cards locally or you can buy them in advance in the Mainland. Open international roaming/Hong Kong, Macao and Taiwan services for mainland mobile phone cards.
How to access the Internet for Mainland Cards At present, only Guangdong users (I can't remember whether Shenzhen or Guangdong is specific) can use the telephone and Internet access functions. Another way is to open international roaming. It's too expensive to surf the internet for one yuan a minute. I suggest Taobao buy a phone card.
Free wifi: There are free WIFI hotspots in many places in Hong Kong, such as buses, McDonald's and shopping malls. 3: China Mobile 18 yuan/day unlimited; China Telecom's 25 yuan/day is unlimited; China Unicom has unlimited 22 yuan/day.
Generally in large shopping malls and restaurants, some even ask the waiter for the password. In addition, in Hong Kong's subway stations, every subway station also has a place to provide free WIFI. 2) Buy a phone card to surf the Internet, and it will be more convenient if you can prepare another mobile phone as a hot spot.