Earlier quoted context omitted.
A good solution nowadays is to ban everything that is not work-related and have people just use their cellphones with their own data plans for that.
No, thats just stupid. A good solution would be a guest WLAN that is, for example, on a separate VLAN. There is no reason to force people to use the slow and expensive cellular network -- both your employees and the people who actually need to use the cellular network will thank you. Also, the GP companies no-peer-to-peer-at-all policy seems... not well thought out, even thought it might be a pretty common policy. Th…
If you run fs_usage against Spotify on OS X, you will see that it is reading files in other places than where it downloads to.