BT has signed a deal with Universal Pictures that will enable broadband users to download movies on the same day as their DVD release.
Inside Man starring Clive Owen is among the films offered
The deal is similar to deals Universal already has in place with DVD rental company Lovefilm and UK website Wippit.
Fans will pay up to £16.99 for a DVD of their chosen film, plus two digital copies to keep indefinitely.
Inside Man, King Kong, American Dreamz and Jarhead are among the titles that will be available from 31 July.
Unlike Lovefilm, BT are not offering downloads to rent as well as own.
However, a rental facility will follow in the autumn when BT launches BT Vision, its pay-for-view TV and film service.
When BT Vision is launched, customers will also be able to download films via a Philips set-top box to watch on their TVs.
Dan Marks, chief executive officer of BT Vision, called the arrangement "a very exciting deal".
The scheme is open to all broadband users in the UK, not just BT customers.
Rob Bell, vice president of digital platforms at Universal, said the deal was similar to those already in place but was "the biggest of its type".
"It sends out a very positive message if someone like BT is getting into this business," he told BBC News.
Simon Morris, Lovefilm's chief marketing officer, said he was "glad" the concept of downloading movies was becoming more established.
However, he said BT was "definitely followers" in a market in which Lovefilm had been "pioneers".
Sky has also launched a broadband service allowing its customers to download films legally.
However, this is limited to titles also available from the Sky Movies pay-per-view service, which usually shows first-run films around three months after their DVD release.