They're not phone specific, but they do contain the account information for each line (phone number, data allowances, etc.). If they are new devices that have never been setup, just put one card in each, they will show you the phone number during setup and you can determine which one is which. If they have been previously set up, you can insert a SIM into one, power up, go to settings>about phone>phone number to determine which SIM you have inserted, then switch if needed.
