Alex Kidd, Gilius, Gum, and Beat were given brand-new dialogue specifically for Sega Superstars Tennis since no pre-existing archival footage was available for use for the characters, being voiced by sound-alikes Jewels Jaselle (female) and Casey Robertson (male).
Sega Superstars Tennis utilizes three voices for the announcer - a male, a female, and a "crazy" voice. All three voices remain uncredited.