At the end of August, Continental will begin flying 737s to Hawai'i. This isn't the first 737 to make the trip, and it's only a temporary move, but it is still very significant in terms of the evolution of the 737.
For years, Hawai'i flying was the domain of widebodies with at least three engines. Without anywhere to stop in between the west coast and Hawai'i, the extra engines provided a sense of security. Eventually, as engine reliability improved, 767s started making the trip. And in the last decade, 757s became the first twin-engine narrowbodies to ply the route, and now they provide the backbone of much of the Hawai'i service out there today.
But 757s are aging and they're no longer in production. What would be able to pick up the slack of this workhorse? Some airlines experimented with 737s in the past few years. Aloha flew 737-700s and ATA flew 737-800s before they both went out of business. They worked well, but in a two-class configuration for a legacy carrier, they didn't carry enough people to make sense. Then came the 737-900.
The 737-900's size was right, but it didn't have the range. When Boeing developed the 737-900ER, Continental saw the opportunity and jumped on it. Continental's ERs can go up to 3,175nm, less than the 757's 3,900nm but still quite useful. I imagine that the range is reduced significantly on long over water flights since extra fuel reserves are required, but this is still enough for plenty of missions currently best suited for the 757.
And now, on August 31, Continental will start flying the ER on the 2,200nm LAX to Honolulu route, at least for a month. Continental has 173 seats on the 900ER, only two fewer than they have on the internationally-configured 757-200. This allows Continental to continue to focus its 757s and 767s on the Transatlantic operation, where they can provide the biggest benefit.
The 757 is now quickly becoming a niche player. It is still the only airplane capable of carrying such a small load to many European cities from the east coast. If Boeing can juice the 737-900 with even more range, then we might see the 757 quietly fade away. For now, it still has an important, but shrinking, role.