NTL has received all necessary court approvals, and Virgin Mobile's shares have now been de-listed from the London Stock Exchange.
Under a previous agreement, NTL Telewest has also entered into a licensing arrangement with Virgin Enterprises allowing the use of the Virgin brand for NTL Telewest's portfolio of consumer services.
NTL said that the acquisition allows it to become the first UK operator to offer a 'quadruple play' of TV, internet, fixed-line and mobile telephony.
The firm added, however, that NTL and Virgin Mobile will continue to operate as separate organisations and brands for the time being, and there will be no immediate change to the services or terms and conditions of either companies' customers.
It is anticipated that NTL will start marketing a single portfolio of services under the Virgin brand some time early in 2007, if not sooner.
Steve Burch, chief executive at NTL Telewest, described the deal as " transformational".
Sir Richard Branson, founder of the Virgin Group, added: "We are entering a pioneering time when the worlds of media, entertainment and communications are coming together.
"Through our new company, our aim is to offer consumers the very best and most sought-after choice available. As the saying goes, you ain't seen nothing yet."
Comcast's £29.7bn winning bid more than twice the £13.7bn Rupert Murdoch valued Sky at just eight years ago
A nuclear strike has been considered, but Bruce Willis is nowhere in sight
Spray-on antenna could enable seamless integration of antennas with everyday objects
Parker Solar Probe, TESS and GOLD missions will deliver exciting data, claims NASA