Paypal really stands out on this one. They are regularly sending me emails with a link to their login page to view my recent transactions (regardless of whether or not there are any transactions). This is clearly negligent.
They're real. They're really real paypal e-mails. Wow.
All messages contain the following "clarification":
"How do I know this is not a Spoof email?
Spoof or 'phishing' emails tend to have generic greetings such as "Dear PayPal member". Emails from PayPal will always contain your full name."
So unless the bad guys can get their hands on a database full of names and email addresses, we're safe. And Paypal can honestly claim that "the security of our customers is very important to us!".
Calling via a landline or via an operator assisted call would make such tricks much more difficult.
Some great papers on Diameter and telco security here: https://www.bell-labs.com/usr/silke.holtmanns
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 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.
Sometimes the one calling you is already suggesting you to do this just to verify. Especially bank and police I noticed.
One thing that I've frequently heard is that in any type of fraud call you should always hang up right at the beginning and call the bank back.
Seems like no matter how sophisticated the attackers, this defense will always foil anything along the same lines of what happened to you. The only way I can see this countermeasure failing is if the scammers can somehow manage to intercept inbound calls to the bank's customer service number.