Irregular Webcomic! #4290

It's not entirely clear to me why you have to say "over" when having a conversation on a radio or walkie-talkie, given that when you talk to someone in person, or indeed over a telephone, it never causes any real problem knowing when someone's finished talking and you can start. I presume it's something to do with push-to-talk and having the incoming audio cut out while you're holding down your own "talk" button. Which probably ultimately has to do with preventing audio feedback.

Or I have no idea what I'm talking about and some walkie-talkie engineer will write in to provide me with excruciating detail that I can edit into this annotation...

EDIT: And within an hour of this comic being published, Sabatino P. writes:

There are many reasons that lead to the necessity of a number of escape sequences in radio communication.
The first is the that the ether medium is shared with anyone who has a radio transmitter; so there is the necessity having a syncro protocol.
Another is the lack, in early transmitters, of an echo cancellation circuit, present in telephone lines, modems, and ethernet (in ethernet on copper it's called hybrid circuit), that permit simultaneous transmission and reception.
A third reason is the economy. The same amplifier devices, tubes or transistor or whatever, and the same antenna, are used for transmission and reception; a unique key command a series of switches that commutes the circuits in transmission mode and reception mode.
On the other side, some high-end radio transmitters consist of two separated apparatuses, one used for transmission the other used for reception; the push-to-talk button joins one or another to the antenna but not at the same time.
Look for simplex, duplex, full duplex, half duplex.