If you need the subsidy to "finance" your phone, then you really can't afford it. Someone mentioned in another thread about the challenge to scrape up $600 for a new phone. I mean, c'mon, you're going to pay $360/yr for data and don't have $600 for a phone? I wouldn't begrudge them the service, but the bottom line is they shouldn't be buying a new phone but getting something cheap on EBAY. I'd guess a fair number of people complaining about losing unlimited data fall into this category and have been using it as an ISP to save money, and losing unlimited means they really can't afford the service if they now have to go pay for home broadband.
The subsidy is $250-$350. Not sure what they really pay, a bit more to Apple, but I think their early termination fee is $350. And $350 is roughly the difference between retail, but VZW isn't paying retail. So let's call it $250 over 20 months...That means on your $30 data plan they are netting about $17.50/month.
VZW is still entitled to a profit after you've "paid" for your device. Their price for data isn't just paying your phone. It's not "buy this phone and get free data". But theoretically, yes, after 24 months your data should go down maybe $10 with the subsidy paid back.