Most major airlines have reciprocal jump seat privileges with each other. Probably not so for fractionals. Jump seat rules are set by the airlines themselves. On some you can ONLY sit in the cockpit while others will let you sit in the cabin. Company pilots usually get 1st priority. Some a/c have more than 1 cockpit jump seat, and so on. I don't know of any airline that has an OFFICIAL reciprocal agreement with any fractional. The majors fly fixed schedules from one terminal to another whereas fractionals usually leave from FBO's. Not a whole bunch of commuters going from Sand Springs, Idaho to Teterboro, New Jersey. I'm not sure how many, if any, jump seats are on the smaller fractional a/c. They sure aren't going to let you sit in the back with the "high rollers".