According to Chris Mannix's twitter account, Rasheed Wallace has retired.
Update: David Aldridge has the story:
The Boston Celtics' expected rebuilding began Thursday when veteran forward Rasheed Wallace officially decided to retire after 15 NBA seasons, a league source said.
Wallace signed a three-year, $18.9 million contract with Boston last summer, turning down offers from Orlando and San Antonio after the Celtics made a team-wide push to recruit him, sending Coach Doc Rivers, GM Danny Ainge and forwards Kevin Garnett and Paul Pierce to Wallace's home to ask him to play in Boston. He left more than $12 million on the table by opting to retire.
More news as it becomes available.