What changes
Instead of inserting a removable card, a supported device downloads a carrier profile. The subscription still needs to be valid and the provider still needs to accept the device. A profile is not a source of extra data on its own.
Setting up
Use reliable internet access and the activation method supplied by the provider. Some flows use an app or device notification; others use a QR code. A screenshot of someone else’s setup is not a replacement for instructions tied to your account.
Two lines on one phone
Choose which line supplies mobile data and which number is used for calls and messages. Check automatic data switching before traveling. Keeping the home line turned on for texts can still have implications under that provider’s roaming rules.
Changing phones
Keep the old device and recovery access until the new profile works. A downloaded profile may need a supported transfer or replacement process. Deleting it does not necessarily cancel the subscription, and scanning an old activation code may not reinstall it.