BT's Call Protect service has been developed to block calls before they reach homes, unlike reactive blocking which may not work when cold callers change their numbers to avoid detection.
Recent data shows BT could divert up to 15 million calls a week from personal accident claims and PPI companies alone.
Users will also be able to compile their own personal blacklist by adding individual unwanted numbers by dialling 1572 after receiving the call or by going online.
Nuisance callers identified by large numbers of customers will also be added to the list.
John Petter, chief executive of BT Consumer, said: "We've been at the forefront of equipping our customers to defend themselves against the huge numbers of PPI and unwanted marketing calls that are continuing to grow.
"Now, with our unique technology, we can identify and tackle huge numbers of those calls in the network and also give our customers control over the calls they receive."
Digital Minister Matt Hancock welcomed the new service in helping customers "fight back against this ongoing harassment".
"Nuisance callers are a terrible blight on society and Government and industry are working together to crack down on them," he said.
"We've forced companies to display their numbers when they call you, made it easier to prosecute those involved in making the calls and increased the maximum fines up to £500,000."
The Call Protect service is available for BT customers to opt into for free.