The appointment, which was made without a pitch, means Fallon will create an integrated consumer and commercial campaign for the company.
The decision to appoint Fallon to handle all UK communications for the mobile phone brand is understood to stem from disappointment within Orange at the quality of creative work coming from Euro RSCG London.
But a source close to the account at Euro RSCG revealed that the majority of work the agency produced was adapted from the creative that came out of BETC Euro RSCG, the Parisian lead agency on the account.
"Orange UK had always indicated that it wanted its business to business to follow consumer communications. Consumer communications in the UK are not the same as in France," the source said.
Euro RSCG London will continue to work on Orange's multinational account.
Fallon has already created a business-to-business campaign for Orange. The work was completed earlier this year, when the agency was appointed to handle a business project for the UK client.
Orange refused to confirm the appointment.