Southwest today firmly ordered 150 B737MAX and thus became the launch customer. Southwest also has 150 options for the MAX. The airline can accept both the -7 and the -8.
Southwest also ordered another 58 B737NG and changed all of their delivieries in 2012 and 2013 from the -700NG to the -800NG.
I think we can expect now some more firm orders for the B737MAX until the end of the year...