Sonic Jam (Game.com) has gone through a few changes over its development process. A couple of the changes are noted below.
These images display different aspects that were changed before the final game was compiled.
Looks like a port of Sonic 3D: Flickies' Island was planned but dropped. This image can be found in a promotional booklet included with the system.
A cutscene similar to this is in the Mega Drive version of Sonic 3 but seems to have been removed. The Game.com port simply starts the player at the beginning of the level in a standing position.