The TV and press campaign will see the debut of Jimmy and Mickey, two Los Angeles University students from 1969, who will become the face of all advertising communications.
CHI has developed a range of ten spots, which use the strapline: "The way the internet was meant to be." The campaign will run over the next seven months.
In the opening ad, the retro duo are seen lamenting how their new invention, an "inter-network", can't be made to work perfectly with the available services. The expertise of BT and the imagination of Yahoo! are then shown turning the dream into reality.
Each execution aims to promote a different service benefit such as speed of connection, personalisation, security and safety, and a soon-to-launch music service.
The joint venture, which replaces the consumer BT Openworld brand, is a direct competitor to the likes of AOL and Freeserve.
"Most advertising in the sector is generic and about speed. To get truly mass-market there needs to be more services promoted," Duncan Ingram, the managing director of BT Openworld, said.
The campaign was written and art directed by Rupert Jordan and Ewan Macmillan.
The TV commercials were directed by Paul Gay through the Paul Weiland Film Company. Media planning was handled by PHD with buying by The Allmond Partnership.
Charles Inge, a creative partner of CHI, said: "The campaign is a real step-change for the ISP market. It is a big idea that is different and very confident."
The Yahoo! roster agency Digitas has developed an online campaign with digital media and buying by the BT roster agency i-level.