The review, which is expected to include territories such as Hungary and Turkey, is said to be procurement-driven out of Vodafone's German office.
It will be handled on a market-by-market basis across "smaller markets" where a review has not taken place for at least three years.
However, it is doubtful that the review will extend to major Western European markets such as the UK.
OMD currently holds a large portion of the Vodafone business in Europe, including the £55 million UK account, and the mobile operator also has relationships with Carat.
The review will not affect OMD's hold on the Vodafone international planning and buying business, which sees buying on international campaigns and sponsorship handled by OMD International in London.
Vodafone announced this week that its chief executive, Arun Sarin, is stepping down after five years at the helm. He will be succeeded in July by the deputy chief executive, Vittorio Colao.
During his time in charge, Sarin has attempted to create a clearer differentiation between Vodafone's global and local activities.