I signed up with an LG Envy II in August 2012. The ETF on my contract is $150 minus $4/mo of completed service. It is now June 2013, so my ETF should be $110 ($150-$40).
If I try to upgrade to an iPhone right now, it will cost me $449 on a discounted pricing.
If I could buy-out my ETF and buy the iPhone with the full discount, it would cost me only $309 ($110 ETF + $199 iPhone).