Use the following steps to add or replace a SIM card in a W1850 adapter:
Remove the SIM door.
Insert an activated 4FF-sized SIM card into the slot marked SIM1 with metal contacts up and notch in. It clicks into place. Depress again to remove, if necessary.
Use the SIM2 slot for a secondary/backup, as needed.
Replace the SIM door and secure with the door screw.