This month, Allen agreed to a multiyear deal worth $3 million annually. He has averaged 5.0 points and 4.8 rebounds in a five-year career.
Whittington played in 20 games last season after making the roster as an undrafted free agent. He was expected to re-sign after competing on Indiana's summer league team.
Robinson played in high school in Indiana and starred at Michigan before leaving school early. His father, Glenn, was the No. 1 overall pick in the 1994 draft.
Christmas, a forward, was acquired in a trade with Cleveland last week.