Opening the cargo doors will get a baggage truck to you at some airports if your scenery settings are on high. Additional default FSX scenery of that kind includes, pressing Shift and F to get a fuel truck coming out to you. However, pressing Control and J when parked at a gate will extend the jetway from the terminal out to your aircraft if you are parked in the correct place. Technically, air stairs are part of the aircraft which is built in to the doorway, so I assume you actually meant the normal mobile passenger stairways of the kind often mounted on a truck or wheels of some sort, which are brought up to the plane.By default FSX can bring a few things up to your aircraft, but not stairs as far as I am aware.
