GS is a request to fly for premium pay. You control the preferences on a GS. IA is crew scheduling telling you what you will do, when and for how long. Both pay double for a lineholder, so if you are able and willing to fly, put in a GS and have a little more control. A bottle of whiskey near the phone in case the wife or kids answer a 404 number is a good technique on your days off. Take a shot, then say hello.