The online ads show the names of famous trios of friends, such as Cuthbert, Dibble and Grub, or Virgil, Parker and Brains, illuminated against a skyline.
Meanwhile, a viral push will target existing O2 customers with an HTML e-shot quiz designed to test how well their friends know them.
Users can either write their own questions, or use O2's suggestions, which include "What's my favourite crisp flavour?" and "What dish would I order in an Indian restaurant?", before sending the questions out to their friends. Although the quiz is designed to reach existing customers, O2 hopes it will also reach potential subscribers as the quiz is passed around groups of friends.
The campaign was written by James Cooper, the creative director at Agency Republic, and art directed by Russ Tucker. Cooper said: "Online quizzes are not new, but daft questions that only your best mates understand have loads of potential."
The online executions, which support above-the-line work rolled out this week by Vallance Carruthers Coleman Priest, will run on youth-oriented lifestyle, mobile phone and music websites including msn.co.uk, yahoo.com and kissfm.com, and comprise overlays, expendable banners and skyscrapers. Media planning and buying is also by Agency Republic.
All of the online communications take users through to a microsite, where they can sign up to the quiz and the "Friends" service.
The campaign launches on 8 October.