Vodafone is calling a pitch for global media account (which is estimated to be worth $600m), having already in-housed chunks of its planning and buying.
The move threatens account holder Wavemaker, which won the brief in 2014 as MEC prior to the Maxus merger. During that time Vodafone internalised a "significant" portion of the business.
In a drive spearheaded by global brand and media director Sara Martins de Oliveira, Vodafone bought most of its digital media buying in-house last summer. It now has internal digital teams serving 11 of its 25 markets.
It's understood the business is looking to appoint a single agency to handle the brief. WPP, among other networks, has been invited to pitch.
The review will cover key markets such as Australia, the UK, India and Spain.
In a statement, the brand said: "Vodafone is undertaking a planned periodic review of its media buying contract in line with good corporate practice.
"We have also significantly in-sourced this activity since the start of the current contract. WPP, our existing supplier, has been invited to re-pitch along with a selection of other large media buying agencies."