The lack of Pokemon locally (at least for now) prevents live testing, but current estimates of data usage center around 5-10MB per hour of game play. Assuming that users play for an average of one hour per day that equates to 150-300MB per month. That might not sound like much, but according to Nielsen total monthly data usage in markets like India and the Philippines were only 1.1-1.2GB?i.e. Pok?mon alone could add additional 25-30% data traffic per Pokemon Go user.
Data usage levels are higher in markets like Malaysia (2.4GB), Indonesia (3.1GB) and Thailand (3.5GB), potentially leading to less stress.