It's a little pouch that has a magnet in it that puts the phone into sleep mode.

That's exactally what it is. A pouch of sort.

Sorry to bring such a beginer question to the forum but I'm new. I have a Blackberry Pearl and I'm looking for the sound options and it gives me an option to change when its in the Holster. What is this holster? Is it just a special carring holster? Can anyone help me? Thanks