You're also not using their service. Is turning your phone off and leaving it in a drawer for a month also breaking the agreement?

If you turn off the phone and leave it in a drawer you will pay the minimum fees. The phone companies are aiming for the maximum. That is having you go over the limits, pay roaming etc. By letting you unlock the phone it opens the door for always receiving only the minimum. This is what they want to avoid.

next big thing:

Credit card companies lobby to make debit cards illegal

Yes they want you to overspend. Their revenue strategy should not depend on it.

You could argue that because the phone is locked to AT&T's network, part of the agreement is that you'll use AT&T's service if you take the phone abroad. Basically, by selling a phone that only works on its network, AT&T is bargaining for the right to any international usage of that particular phone, if there is any.

This is a very common contractual scenario--you get a discount for agreeing to only use one particular vendor, to the extent that you have a need for the particular kind of service they provide.

Well, not only are you not using their service, you're using somebody else's service when theirs is available.

As per your binding contract, you agree to only use their service in return for getting the phone at a subsidized price. Their incentive to charge you less for the handset (incurring a loss on the sale) is that you agree to guarantee doing business with them.

And if that's a problem, unlocked phones are still always an option.

"As per your binding contract, you agree to only use their service in return for getting the phone at a subsidized price."

You mistakenly believe that contracts are in perpetuity.

You're suggesting Protectionism. An industry won't innovate or provide realistic pricing based on their actual costs, so you suggest we protect their income through artificial means. Sure, I'd love some protectionism - how big do I have to be before the government will invent some laws for me to make sure you can only use my service, and not yours?

Honestly I'm not suggesting anything. All I'm saying is that this contract is optional. People can buy full price and say fuck-you to the contract. In fact I have gotten iPhones cheaper from AT&T by buying locked and immediately buying out the contract than buying unlocked from Apple.

>In fact I have gotten iPhones cheaper from AT&T by buying locked

In which case I'm sure we'd all consider it reasonable to first ensure AT&T covers it's cost by increasing its contract buyout amount. We're talking here about the price of roaming being artificially high. You step across the border and come back to an inflated bill because of termination 'agreements' between providers.