There seems to be broad consensus amongst the commenters that this is the most reliable defense against this kind of attack. Makes sense. If they are able to intercept my outbound calls, it's probably an entirely different level of sophistication and targeting.
I read about a landline attack that would keep the line open when you put the receiver down, play a dial tone, and then wait until you’d entered a number before putting you back on with the scammer
Analogue telephones are creating (or at least in modern times simulating) a circuit, which doesn't close until the caller hangs up.
But almost everybody today has a digital phone, any kind of mobile telephone or desk VoIP phone is digital, "hanging up" ends the call because the telephone itself decided to do that, everything is just packets. So this trick won't be effective against most people today.
Likewise "dialling" today is an out-of-band digital step rather than a bunch of pulses or tones sent in-band that an attacker can just ignore.
> I read about a landline attack that would keep the line open when you put the receiver down
I experienced this once, but not as a scam, I think there must have been some kind of fault at the exchange... the other end was a mobile phone and they didn't end the call, just putting the phone back in their pocket - the landline wouldn't disconnect, whatever signal was send, even disconnecting the phone entirely and plunging it back in. I didn't understand how exactly, but it made it pretty clear the (landline) telephone is not in control of the connection.
