What does the mobile phone card mean by monthly subscription?

The monthly rent of mobile phone card is the monthly fee that users have to pay to ensure the normal use of mobile phone card.

Mobile phone cards generally refer to SIM cards. SIM card is the abbreviation of subscriber identity module, also known as subscriber identity card and smart card. GSM digital mobile phone can only use this card. Digital mobile phone customer information, encryption key and user phone book are stored on the computer chip, which can be used to authenticate the identity of GSM network customers and encrypt the voice information when customers talk.