How eSIMs work: downloadable profiles stored on the phone's built-in chip

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An eSIM is not a physical card but a downloadable profile installed on the eUICC chip that phones already contain. Users typically activate one by scanning a QR code or entering an operator-supplied code, after which the profile carries the operator's identifiers and keys. Several profiles can be stored on the same chip and switched between through a settings toggle rather than a physical swap. The article stresses that the eSIM is only a container, so roaming, throttling and top-up behaviour depend on the operator behind the profile, which explains why similar plans can perform differently.

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