Fraudsters are abusing "call clearing" systems that keep a line open even if the person being called has hung up.
The system was first brought in to make it easy to transfer calls to extensions in homes.
But hi-tech thieves are abusing the lengthy delays to trick people into thinking they are talking to a bank or the police.
Call clearing times can stretch to two or three minutes on some UK networks but the need for this was shrinking, said a BT spokesman. Fewer people now had a requirement to shift calls to extensions in their homes, he said, thanks to the popularity of cordless phones.
However, he said, all UK operators and industry watchdog Ofcom had noticed an increase in fraud that is based around the lengthy call clearing times.
Typically, a conman trying to abuse this feature would call a victim pretending to be from their bank, ISP or even the police informing them about an issue that requires them to supply credit card details. The conman will tell the victim to verify that the alert is genuine by ringing another number.
However, if the call is made from the same phone line before the call clearing deadline has passed, the caller will still be connected to the fraudster who can trick them into thinking the verification is genuine and card details must be passed on.
BT, Sky and Virgin Media have all outlined plans to cut call clearing times from minutes to seconds to thwart thieves. TalkTalk said it reduced its call clearing times "a good few months ago".
In a statement BT said: "We intend to cut the 'holding the line open' time to two seconds and we will have a solution in place to do this for several million customers over the next six weeks.
"We need to do some further testing for the remaining lines and will resolve this issue for those customers as soon as possible."
Virgin said it was working on ways to cut clearing times on its network.
Emma Hutchinson, a Virgin Media spokeswoman, said: "If someone is concerned about a call they've received, they should hang up and either wait five minutes or use another line to speak to the police on 101."
Rising fraud has prompted UK phone operators to tweak their networks to remove features exploited by criminals.