How does a carrier manages to make an iOS feature unavailable for it's customers unless they pay for it? Is it a factory setting on region specific iPhones? Is it that iOS is "polite" and checks if the carrier allows, for example, tethering before allowing you to switch it on? What's to prevent a greedy carrier to say: Ah, you want to use the phone's address book? It's gonna be another $10/month. I am curious as to what would happen for those of us that own an unsubsidized, factory unlocked phone bought directly from apple. Presumably, no carrier has been able to put its dirty hands on it to restrict what it can do. If we go to the US and start to roam data using our non-US sim card. Can we switch on internet tethering if our home provider allows us to do it at home? (considering that ATT charges $20/month for it) Or if one just get a prepaid US sim card with 3G data (if possible at all) with the same factory unlocked phone, what happens? And what if you move to the US with your phone and get a contract there, will they modify your phone when you activate the new sim? How do they check / enforce that? Sorry if this has been asked before, I didn't managed to find an answer with the keywords I used.