The Croatian agency beat to the contract competitors from Ukraine, Russia and Turkey, Croatian daily Poslovni Dnevnik (www.poslovni.hr) reported.
The value of the deal was not disclosed.
Bruketa&ZinicOM will be in charge of the telco's overall communication strategy.
The Croatian advertising agency, set up in 1995, employs 60 at its two subsidiaries.
Nar Mobile, launched in 2007, has more than 1.3 million subscribers.