A:Answer You only buy the SIM card once. It does NOT provide phone service. All billing and payments are through your Google Fi account. To get phone service, you create an account with Google Fi. Transfer your current phone number, or get a new number, through your Google Fi account. You put the SIM card in your phone when you activate service, then Google Fi tells the SIM card what your phone number is and other info it needs for your phone to work. Google Fi will also give you a $10 credit on your bill, so you will get back most of the money for the cost for the SIM card.