[ChuckMcM]

Add a bit of personal experience here. Google gave its employees unlocked Android phones (not once but twice :-) and some of us (like me), put our AT&T sim card into them and used them instead of our plan phone. There was a 'feature phone' data plan that was $15 unlimited and there was the $10/month 'tax' if you had an iPhone.

Using the cheaper unlimited plan worked for a long time, and then AT&T started 'automatically' switching people to the smartphone tax if their IMEI indicated they had an android phone. I did what any reasonable person would do, cancelled my AT&T contract and signed up with t-mobile :-)