Using an existing large-scale realistic discrete event simulation model of a mobile distributed system we model the infrastructure and dependencies of 2G, 3G and 4G mobile data networks. We investigate the effects of the different network generations and of transitioning connections between networks on the typical behaviour of the distributed system. In particular we enable the model to simulate regional outages of networks to predict the effects of shared back-end network components and the effects of mobile endpoints entering and leaving regional coverage.