In Terminator 3, the Terminatrix connected to the police network by whistling modem noises into the phone. Is that actually possible?

Could be. Long ago when everyone used rotary phones, I was horsing around one time. I could hear the dial tone pulse as the dial went around. I decided to see if I could imitate that by clicking the buttons which hang it up. I tried to use a rhythm which sounded similar. I called somebody, but I don’t know who. They didn’t speak my language!

I don’t see why it would be a problem. Based on previous Terminator models, they apparently have the ability to successfully impersonate any human voice flawlessly.

I remember a scene in one of the previous movies where a male Terminator spoke over the telephone in a female voice familiar to Sarah to lure her out of hiding.

Since human voices are more nuanced and difficult, I don’t see why a Terminator (a machine) would have any difficulty to mimic machine tones. Should be easy.

Yes. Why not?

If the police network still had old style modems, then calling in and speaking modem tones would work. A modem MOdulates computer commands into tones and DE-Modulates tones back into computer commands. That’s where the name MODEM comes from.

It’s like @RocketGuy said. Basically, it’s a variation on phreaking. Any system that uses sound to verify a connection can be fooled by replicating those sounds.

Back in the day, before the first Apple was built in the garage, Steve Jobs and Woz built these boxes which enabled users to make free calls all over the place from pay phones by imitating those tones. They were selling them through word of mouth.

Fortunately, they eventually turned their attention to building personal computers instead :)

Used to be, yes.

Modem stood for modulator-demodulator. All it did was translate data into sounds that could go through the phone lines and back again from sound to data. So technically, as long as she had the ability to translate it back, she could very well be communicating doing that.