  Mobile messaging services have gained a large share in global
telecommunications. Unlike conventional services like phone calls, text
messages or email, they do not feature a standardized environment enabling a
federated and potentially local service architecture. We present an extensive
and large-scale analysis of communication patterns for four popular mobile
messaging services between 28 countries and analyze the locality of
communication and the resulting impact on user privacy. We show that server
architectures for mobile messaging services are highly centralized in single
countries. This forces messages to drastically deviate from a direct
communication path, enabling hosting and transfer countries to potentially
intercept and censor traffic. To conduct this work, we developed a measurement
framework to analyze traffic of such mobile messaging services. It allows to
conduct automated experiments with mobile messaging applications, is
transparent to those applications and does not require any modifications to the
applications.
