Unscrew and detach the modem door of the W2005.
Insert the SIM into the slot marked SIM1 with metal contacts up and notch in. It will click into place.
To remove, depress again.
Use the SIM2 slot for secondary/backup.
Replace the modem cover and secure with the modem door screws.
Important
Please note that modems do not power themselves off when the SIM door is removed. If you need to swap SIM cards between the two slots, or replace one or both SIMs on a powered device, Cradlepoint strongly recommends that you power off the W2005 before removing the SIM door. Re-attaching a SIM door on a powered device automatically resets the modem, and you must NOT power off your device during a modem reset. Powering off your device during a modem reset can cause the modem to become unbootable.