I think the base on-contract price of the phone will just increase (e.g. lower subsidy). Fido, my provider, offers the Samsung Galaxy S4 for $200 on a 3-year contract, or $449 on a 2-year contract. I expect the iPhone would be priced similarly.
Before smartphones, most people expected a cell phone to cost between $0-100 on contract. They needed aggressive subsidies to prevent people from balking at the cost, and therefore longer contracts to keep people from reneging on their commitment. Today people understand that smartphones can cost $200-$400 on-contract, so there is no longer such a need to keep initial sticker shock down.
Monthly plans may also go up. Fido offers a $39 plan for 2-year-contract signers, but the equivalent plan on a 3-year contract is $50. If you choose an Android device, you can pick whether you want a 2-year or 3-year contract, but if you choose an iPhone, you must take the 3-year plan. Obviously the extra fee is to recover more of the subsidy over the extra year. If that extra year is no longer an option due to these new rules, then either the plan prices go up (no more $39 plan) or the initial phone jump.
I hope these guys understand that shortening to a two-year contract can be a GOOD thing. Don't they want me giving them an extra $200 or $449 every two years instead of every three?