After a three-day trip to Hong Kong, I heard that I can buy a phone card for 50 Hong Kong dollars. Excuse me, can this card be inserted into a mobile phone, and can iphone be used?

Yes, you can. You can buy it from Taobao. Or buy it at the pass, less than 50 yuan, more than 30 RMB. There are some phone bills in it, which will last you three days. They are all sim cards, not small iphone cards, but you can cut them anywhere. If you don't use the phone bill in your card, you can deduct HK$ 2 every month. If you don't use them, you can keep them for next time. I made two useless cards and I still have them with me.