Agencies were judged on the strength of their planning credentials, particularly as 3 prepares to mount a challenger campaign to a crowded market dominated by Vodafone, T-Mobile and O2.
John Penberthy-Smith, the marketing director of 3, said: "We're looking at a campaign that reflects our new sense of confidence, and forces people to reappraise the brand. 3 is a challenger brand and we wanted to work with a team that is using its experience to challenge the norms in the world of communications."
A 3 spokesman added that it had not ruled out assigning glue London for digital projects.
The pitch, overseen by ISBA, is Euro RSCG's first major UK win since Mark Cadman and Russ Lidstone became the chief executive and chief strategy officer respectively in May 2006.
The appointment comes as 3 looks to put behind its difficult launch in 2003 that saw customers complain about inadequate network coverage, poor service and a dearth of handsets. Incumbent agencyWCRS handled its launch.