The antenna is basic anatomical part of most, if not all, robots. While most people believe the antenna to be purely aesthetic, to make them look more "science fiction-y", they actually function as receivers for Mom's universal robot controller, as revealed in the episode Mother's Day.
Each robot seems to have different secondary uses for it, though it is often hinted to be the robot equivalent of a penis.
In I, Roommate it is revealed that robot antennae (or at least, Bender's) interfere with satellite televisions and cellphone reception.
In addition to the uses mentioned above, Bender's antenna has been used for several other purposes throughout the show, including (sorted by first appearance):
- Butter dispenser (Fear of a Bot Planet)
- Music play button (My Three Suns) - function unclear
- Beer dispenser (Hell is Other Robots)
- Halo holder (Hell is Other Robots) - questionable
- Timer for camera (When Aliens Attack)
- Receiver activated by the miliatary to instill patriotism (When Aliens Attack)
- Inlet to pour drinks for cocktail making (A Head in the Polls, The Route of All Evil, Simpsorama, for yeast)
- Bomb explosion indicator (War is the H-Word)
- Installation status indicator (The Honking)
- Toilet flush (The Cyber House Rules)
- General receiver (Anthology of Interest II) - within a "What-if" scene
- Microwave readiness indicator (The 30% Iron Chef)
- Voicemail deletion trigger (Kif Gets Knocked Up a Notch)
- Pager (Less than Hero, The Mutants Are Revolting)
- Laser ball (Jurassic Bark)
- Magic prop that can turn into flowers (Jurassic Bark)
- "New Mail" indicator (Crimes of the Hot)
- Activation switch for binary code mode (Bender's Big Score)
- Presentation pointer (Ghost in the Machines)
- Cigarette lighter (Fry Am the Egg Man)
- Cannon fuse (All the Presidents' Heads, Cold Warriors)
- Cigar dispenser (Reincarnation)
This list doesn't include Bender using them in ways that aren't a specific "feature" such as a skewer, lightning rod, etc.