Since we're all being humble, I'll stick my neck out at the risk of being wrong...
As I understand it, all but the early NG737's are capable of ETOPS certification so if WN wanted to fly to HI they have the airplanes with more coming.
Jim
Actually, Jim, the original 737NG's were used on the proving runs for Aloha's service between the mainland and Hawaii. We discussed, ad nauseum, the "rumor" of Southwest starting service to HNL, after one of our "Desert Gold" birds landed there in '97.
I would like to say that I prefer this communication model, however.