The Wall Street Journal says that Apple is working on a cheaper version of the iPhone, following an earlier report from Digitimes. According to the Digitimes report the device may have a larger screen than the current iPhone 5, and the Journal says it could come as early as late 2013. The Journal has an excellent record with the accuracy of its Apple rumors, posting accurate information on products such as the iPhone 5 and iPad mini ahead of their official announcements.
The report says that the phone may use a design similar to the current iPhone but with cheaper parts, such as a polycarbonate body to replace the iPhone 5's aluminum. There is, however, a disclaimer that Apple may decide against proceeding with the device. Any such device would certainly represent a major shift in Apple's product strategy; Cupertino currently offers the iPhone 4 for free with a two-year contract, but doesn't have any inexpensive unlocked phones — a major hole in its lineup for several global markets.
Update: Bloomberg has also chimed in, saying that it expects this new low-cost iPhone to cost between $99 and $149 — a pretty obvious price point considering iPhone's longstanding $199 cost. That said, if it hits that price without the usual carrier subsidies, it would be a pretty major development indeed.