My latest bill included a note that they're changing the upgrade eligibility for subsidized phones from 20 months to 24 months. Honestly it seems pretty stupid to me, they should have at least changed it back to 22 months. Getting people to renew BEFORE their contract expires is a great way to keep people from jumping ship, and Sprint needs all the help they can get with retention.
Think about it like the average customer: currently a customer gets a notice that they can get a new phone. They might look at other carriers, but they'd have to wait four more months or pay an ETF to get a new shiny phone. That's a pretty big incentive to stay. Under the new plan, when a customer is eligible for a new phone they could either stay with Sprint or port to T-Mobile (which they keep seeing all these blogs raving about how great they are) or Verizon (which is offering a $150 credit to port in your number). Suddenly Sprint doesn't seem like such a hot deal.