I have had two people claim they were called pre airport after volunteering during OLCI but I am of a belief that said folks were not really on delta though both claim it was delta so I think the only way to get selected is to go to the airport and let the ga know you are happy to volunteer. Then be listening for a request for volunteers sometimes they forget those that have asked early on. Not sure it is really worth the hassle of dealing with Lga and I think chances are slim if you don't go to the airport