Follow this guide to install a SIM card in the Blackberry Pearl 8100.
Begin by removing the back panel; this can be done by pressing the silver button on the backside of the Blackberry 8100, while simultaneously sliding the back panel off.
Remove the battery located directly below back panel.
Slide the larger of the two metal casings upward (in the direction pointed to as “unlock”).
Lift the metal casing.
Insert an SD Card.