1. A collector device for real-time, transparent monitoring of application-level data activity on a mobile data network, the collector device being in communication with a corresponding mobile data network router, the collector device comprising: an input coupled to the network router and configured to receive substantially all data communications from the network router, wherein the data communications include application-level data relating to specific users' use of applications on corresponding user mobile devices; a user identity subsystem, coupled to the input, for correlating phone numbers associated with the user mobile devices with IP addresses and the application-level data, wherein the user identity subsystem modifies the correlation of phone numbers to IP addresses and application-level data in response to the detection of new IP address assignments for the corresponding phone number; a filter subsystem configured to: receive the substantially all data communications from the network router and retain only application-level data; identify session requests in the application-level data from the specific users' use of the applications on the user mobile devices; parse at least one of a uniform resource locator (URL) and a user agent in each of the session requests to identify specific destinations requested therein; using information parsed from at least one of the URL and the user agent to classify a content type of a webpage associated with the content requested in each of the session requests; and a demographics subsystem to determine demographic information to associate with each of the specific user's phone numbers, the demographics module determines the demographic information using the correlated phone numbers.