to choose Unicom 3G package, you need to sign up and register user information, and users who use the form of first use and then pay monthly fees are 3G post-paid users.

For example, some post-paid users don't stop the phone immediately when there is no phone bill in their accounts, but some post-paid users have a certain credit line. When there is no phone bill in your account, you can overdraw this credit line, just like a credit card. For example, if your credit line is 1, you can overdraw the phone bill in 1 yuan and continue to use it after your phone bill is used up, and stop when the credit line in 1 yuan runs out.