What does a locked SIM card mean for a smartphone?

A locked SIM card indicates that the smartphone is configured to restrict the use of certain SIM cards. When a phone is locked to a specific carrier, it means that only SIM cards from that carrier can be used to access the network services. This is a common practice among mobile carriers, often used when a phone is sold at a subsidized price or as part of a contract.

In contrast, if the SIM card were physically damaged, the smartphone would likely be unable to recognize it at all, which would not fit the definition of a 'locked' SIM card. Similarly, the phone being unable to access any network would suggest issues such as service outages or unregistered SIMs, rather than a lock condition. Lastly, while a locked SIM card could potentially lead to issues with internet connectivity if a user tries to insert an unsupported SIM, it does not directly mean that there is no internet connectivity overall. The fundamental aspect of a locked SIM card is the restriction placed on using alternative carrier SIMs, thus justifying the selection of this answer.