According to the recent rumors (again), a Low Cost iPhone is finally headed to the market this year. However, unlike in the past I do believe the cheap iPhone is coming this time for one reason only. 

T-Mobile is rumored to get the new iPhone and they are getting rid of subsidies. Yes Apple currently sells unlocked iPhones, but I do not believe T-Mobile expects people to pay the current iPhone full price and gain a large market share. The timing just fits perfectly. Only time will tell if the rumors end up being true.