The process of getting a SIM card activated on your iPhone can be confusing. The majority of people have no idea what the ‘msid’ or ‘media device identifier’ is, where it comes from, or why it’s needed.
The media device identifier (msid) is a unique number assigned to all SIM cards by the manufacturer. It’s used for identifying the card to the network and verifying that it hasn’t been tampered with or modified.
Apple uses this number to activate your iPhone’s SIM card when it detects that you’ve changed carriers. If you want to use an existing SIM card in one of these situations, you need to provide Apple with its msid so that they can activate it properly.
Last modified: November 21, 2022