A method and apparatus for determining the impact of a software upgrade on a service performance are disclosed. The method obtains call detail records associated with a plurality of mobile user endpoint devices, aggregates each mobile user endpoint device into at least one group, maps each mobile user endpoint device to at least one first aggregate, wherein each aggregate of the at least one first aggregate comprises at least one of: a group established based on the type of each of the mobile user endpoint devices, a group established based on the make of each of the mobile user endpoint devices, or a group established based on the model of each of the mobile user endpoint devices, and identifies a nearest co-occurring software upgrade when a change in a service performance in the communications network is detected based on the at least one first aggregate.