What can the primary card see from the secondary card?

It can see call records, short messages, phone bill balance, package usage and so on.

The primary card and the secondary card are two different packages under the same account, sharing the same phone bill balance and package resources. Therefore, the main card can see the call records and short messages of the secondary card to understand the usage of the secondary card. In addition, the main card can also know the package usage of the secondary card by querying its account information, such as the remaining traffic in the package and the call duration. If the supplementary card uses more resources than the package, the main card will also receive corresponding reminders or notifications.