According to the latest chatter from the Wall Street Journal, Apple has decided that size does matter and will offer a second, larger screen iPhone later this year in order to compete with market pressure from Samsung et al. Thus, you can expect 5-inch an iPhone to land sometime around Apple Christmastime in September.
The Journal's sources claim Apple's next phone, which we can safely assume will be called the iPhone 6 or 6s or 6c, will be metal like the current model and will be offered in two sizes: the current 4-inch size and a bigger 5-inch one. After only one colorful year, the plastic case on the 5c is apparently disappearing due to low demand for pastel colors.
Although big screens have been catching on stateside with Android devices with 5 and 5.7-inch screens, Apple's big move may be a play to get more Chinese users on to iPhones. Apple just started selling the devices in China last week and according to the WSJ, "bigger screens are particularly popular" with that market.