First off we do not know the cost of the phone to the providers, but the cost of even the newest available iPhone is less than $200 for Apple to produce. Figure in all their other stuff and they can sell it profitably at $250. I doubt AT&T even pays $250 per phone yet the ETF is far in excess of the cost to them.
Secondly the ETF is more about consumer retention than it is about recovering the cost of a subsidized phone. This is clear in many respects 1.) ETF's have been raising, yet the true cost of phones have been dropping 2.) The ETF still has a substantial balance even in the last month of the ETF period 3.) Service plan prices do not change regardless of whether or not you fully own the phone because you purchased it outright or have been using it beyond the initial 2 year agreement.
I personally think the only thing a user should be under contract for is the phone itself. You either purchase it outright or you finance it. Then you can take it to any compatible service provider and pay for their service WITHOUT any term obligations. If their service does not meet your expectations then you go to another provider. That is letting the market decide on both the phones and the provider.