The post at https://android.stackexchange.com/questions/47819/how-can-phone-companies-detect-tethering-incl-wifi-hotspot https://android.stackexchange.com/quest

The post at https://android.stackexchange.com/questions/47819/how-can-phone-companies-detect-tethering-incl-wifi-hotspot https://android.stackexchange.com/questions/47819/how-can-ph... offers some explanations. I'm pretty sure I've come across different APNs being used before (on the Giffgaff MVNO using O2s UK network), but don't recall the details.