Supporting Nokia's 7610 handset, the TV and digital campaign will run in 10 different languages through a constant feed of content for over six weeks.
The TV spot introduces three characters Anna, Jade and Luca, starting with intrigue about one of them having listened to another's voicemail and sets the scene for how their lives might unfold.
Fans will be able to learn everything about the characters through their text messages, photos, videos and calls on somebodyelsesphone.com, as well as signing up to their Facebook pages to have a more personal conversation.
Nokia aims to re-engage a younger audience with the campaign, which includes TV, print, outdoor and radio along with the digital element.
The microsite is supported by mobile content, interactive partnerships, widgets, Facebook pages, banner ads and a number of events in association with partners including Parisian boutique Colette.
At the end of the six weeks, the characters' stories will confront crucial decisions that will affect their future.
These questions will be shared with the audience, giving them the opportunity to influence the storylines themselves.
A goodbye from each character will then be revealed a few weeks after the campaign finale event on December 11 in Paris, when competition winners will have the chance to meet the cast.
Matt Gooden, creative director at Wieden & Kennedy, said: "From a personal point of view I've loved working with drama script writers developing longer format story lines and for W&K, it's been a chance to really dig into our digital capabilities."