I only ask, because routing everything over a VPN provides the illusion of privacy while flipping contracts every month provides some element of real privacy. It is easy enough to check on the activity of people pretending to hide their activity (assuming GCHQ has access to the same access that the NSA do), but real resources have to be spent tracking down people who actually hide their activity.

I have no idea how they allocate their budget for tracking potential threats, but somebody flipping prepaid sims would warrant a closer look if I was analysing the logs.