Delta is adding non-stop service to Phoenix starting in December at once daily using a 739.
Boston to Phoenix leaves at 8:00 am and arrive at 12:14 pm
Phoenix to Boston leaves at 11:45 pm and arrives at 6:54 am
No official press release, a user in the Delta network thread over on Airliners.net posted it. Flights are bookable.
Between Denver, Baltimore/Washington, San Diego, Dallas/Ft. Worth, and Kansas City either recently starting, or due to start, Houston is the only hole in what has become a solid domestic network for Delta.