MediaCom has been awarded the media planning and buying business following a competitive pitch.
Y&R saw off competition from Saatchi & Saatchi and Mother to clinch the business, which is worth an estimated £30 million.
Banner Corporation, the Y&R subsidiary that specialises in technology brands, will handle the creative work in the UK to avoid any conflict issues with Virgin Mobile, a client of Rainey Kelly Campbell Roalfe/Y&R.
FreeMove, which was established at the beginning of the year through a collaboration between T-Mobile, Orange, Telefonica Moviles and Telecom Italia Mobile, offers a range of standardised mobile services, including improved international roaming for subscribers to the partner networks, next-generation data and a single tariff. It has a combined reach of 170 million customers across Europe.
Plans to extend the service to Asia-Pacific and the US, where T-Mobile has a significant presence, are currently under consideration.
A multimedia campaign to introduce FreeMove to the public - initially in the UK, Italy, Germany and Spain - is scheduled to launch before the end of the year.
It is expected to be led by an aggressive TV push as the alliance looks to fight Vodafone for the top spot in the telecommunications division.
Vodafone currently dominates the market; in the UK alone, it has more than 13 million registered customers and a 7 per cent lead over its closest competitor in terms of mobile service revenue share for outbound calls.
The new brand will highlight the benefits it provides for its customers travelling abroad, while also establishing itself as a quality mark in each of the members' domestic markets. The FreeMove logo is already being incorporated into Orange advertising in the UK.
FreeMove initially approached the roster agencies from all four of the alliance's networks with the brief. Y&R was included because its handles Telefonica in several European and South American markets, as well as Telecom Italia.
William Eccleshare, the chairman and chief executive of Y&R and Wunderman Europe, the Middle East and Africa, said: "I can confirm that Y&R has been awarded this very significant assignment across Europe. If you look at the FreeMove offering, you will see why we are so enthusiastic about it - it's a brilliant concept with enormous benefits to customers."