The sixi card you mentioned is a telecom service, and the monthly caller ID only charges three yuan, which is the call charge in 5 yuan (that is, the minimum consumption is 50 minutes). This card is most suitable if you just answer the phone and call occasionally.
If you don't call directly or only give you a number, it is recommended to apply for an E-Pass card, which is often called a ternary card. It only charges three yuan a month for caller ID, and there is no extra charge. This card can also be bound to a telecom home number, and national calls are free. As long as you are not in Hong Kong, Macao and Taiwan.
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