[rfonseca]

Also, don't call from the same phone you received the call on, if on a landline. One time (I can't find the reference) scammers called from the bank, suggested the person called back to the number on their credit card. The person hung up, picked up, and the scammers had held the line, played a fake dial tone, and had someone else "pick up".

[IIsi50MHz]

In USA telephones, unless you timetravel to "party lines" (when sets of local numbers had the same line, so picking up while a call was in use allowed people to listen or join in), hanging up any one end of a line disconnects the call the departing user from the call.

If the described scam happened, in should have required a simultaneous fault in the phone system. Or more likley, the scammer played a recorded sound of a disconnect+dialtone, which could tricker the target into dialing.

[aidenn0]

This is incorrect at least on Bell Atlantic's (and then Verizon's) network in the late 90s. Since there is no double-billing on landlines in the US, the person initiating the call is the only one that can immediately terminate a call to a landline. There's a timeout for the reverse direction, but it at least used to be fairly long.

Someone pulled a trick where they took advantage of this. Had a friend call and keep the line open. Then claim that you have the entire phone book memorized. To prove it, ask someone to name a random name, punch in 7 digits and hand it off to the person who named it. They ask for the name and your friend says "yes that's me" (or "they're not home now if the gender mismatches).

[toast0]

The time required for a good hangup might vary a little bit from exchange to exchange. I recall occasionally being able to transfer to different handsets hanging up one before picking up the other. But not to the extent reported in some anecdotes where one end can hold the call open indefinitely.

[NoZebra120vClip]

IIRC, the originating party's on-hook will immediately disconnect the call, while if the receiving party goes on-hook, there is a short but significant delay before disconnect is finalized.

This may have something to do with service offerings such as call-waiting and 3-way, which depend on detecting a "flash" signal.

[Mordisquitos]

I believe that potential exploit only work(s|ed) in the UK telephone network, and maybe those of countries developed in parallel using similar technology. Either way, it is a zero-cost precaution so you might as well do it just in case.

[dudul]

What? Where do phones work like that? Isn't it enough for one party to hang up for the call to be over?

[ralferoo]

They used to operate this way in the UK - the line would stay occupied until the call initiator hung up. We used to play with this when I was a kid, but I've not had a landline since early 2000s, so I've no idea if this survived the transition to digital exchanges. TBH I doubt it, and I know lots of people complained about it, because it was really annoying if someone who'd called you hadn't hung up properly as then you couldn't make any further calls yourself.