Merynkaw,
When you purchased the system, did it come with the sim card already installed? If you're not sure, go to Dell Warranty Status enter your service tag, click on original configuration. It would be listed there.
The question I ask is the slot is there for all computers for your model, but if it was not ordered, the slot wil not have any hardware for the sim card, so basically it's a blank slot without the hardware.
Rick