Southwest Airlines became the first customer to place a firm order for 737 MAX. The press release is here. First delivery is 2017.
Southwest had been urging Boeing to proceed with the re-engine for two years, only to watch American Airlines become the first company to commit to the MAX last July.
Southwest has ordered more 737s than any other customer. It was the launch customer (and operator) of the 737-300/500/700.
Southwest’s delivery schedule for the MAX is here.