It is understood that Glafkos Persianis, Vodafone’s new UK commercial director, is looking to change its marketing strategy and focus on the telecoms giant’s core service rather than additional benefits, as it battles to close the gap on bigger rivals EE and O2.
WPP has a close relationship with Vodafone, handling both the brand’s creative and media activity.
Grey picked up the ad business from sister WPP shop Rainey Kelly Campbell Roalfe/Y&R in February last year.
However, Vodafone has contacted non-WPP creative agencies.
Any review will be a blow for Grey, which lost News UK in December last year and had to shuffle its management team after chairman and chief creative officer Nils Leonard, chief executive Lucy Jameson and managing director Natalie Graeme quit. They are expected to launch a start-up.
However, new chief executive Leo Rayman received a boost when Grey won Marks & Spencer in August.
MEC picked up Vodafone’s global £600m media account in 2014.
The Vodafone Christmas campaign, created by Grey and filmed in a pub in Oxford, launched this week.
Vodafone declined to comment.