Disclosed herein are methods and systems for detecting congestion in a mobile network and for determining those end-user mobile devices that are affected. In one embodiment, a server communicates with a set of mobile devices, on which have been installed a suitable client application. At certain times, the server initiates a congestion detection routine. The server may request the mobile devices to report on their current wireless attachment point to the mobile network. The server can then test for congestion by performing a data transfer between itself and the mobile clients, which may be in either direction. The server can use the results to determine whether a given attachment point is congested. In one embodiment, a dynamically selected, random subset of mobile devices for a current attachment point are tested, and the result is imputed to all mobile devices similarly situated.