the sim card is not for use with an actual sim card used for phones. the sim card used is a strict Data only card. if your laptop has an accessable sim card slot and you havent had to change your harddrive (meaning you are still useing the one that came with the laptop) and have not had to wipe it clean then all you need to do is find a carrier that will send you sim card that is strictly for laptop data use. you will need to pay it like anyother montly phone bill.
Per the other posts the SIM card slot is simply there due to the fact that some versions of your notebook have active cellular modems. Yours does not, the the SIM card slot does not attach to the MB electronically, the slot is just molded in as part of the notebook chassis hardware.
The easiest way to get your notebook to work using your carrier bandwidth is to activate the wireless router mode of your smartphone and have it serve the notebook via wifi. My carrier Verizon offers this option for around a dollar or so a day. It has a 5 gig monthly limit and does not use your phones data plan. You can activate or deactivate the plan as you wish. This normally does require a newer smartphone that can act as a wireless router using the carrier data feed.
My HP Elitebook has a SIM slot, even though I don’t have the cellular data module. But the slot for it is right above the wi-fi module slot, and it has cables for the cell antenna.