In Super Monkey Ball 3D for the DS, there are several characters you can unlock by doing certain things. Here are the characters you can unlock, and how to unlock them.
A-Baby – Finish second in Sky-Way
B-Jet – Finish first in Mt. Tyrano
F-GonGon – Finish third in Mt. Tyrano
N-Jam – Finish first in Sky-Way
P-YanYan – Finish second in Mt. Tyrano
R-Doctor – Finish third in Sky-Way