The moves Wednesday increased the team's roster to 18 players.
The 6-foot-10 Sims averaged 8.0 points and 4.9 rebounds in 73 games last season for the Philadelphia 76ers. The former Georgetown player has averaged 7.8 points and 4.9 rebounds in 121 career games in three seasons with New Orleans, Cleveland and Philadelphia.
The 6-9 Jefferson averaged 3.7 points, 2.9 rebounds and 10.6 minutes in 50 games as a rookie last season with the Brooklyn Nets. The former Baylor player was drafted 60th overall in 2014.
Casey, Burton and White played in Europe last season. Casey played for KK Helios Suns Domzale in Slovenia, Burton for Ratiopharm Ulm in Germany, and White for Yenisey Krasnoyarsk. Burton played at Nevada, Casey at Harvard, and White at Mississippi.