As noted in the report, such testing doesn't mean the devices will ever hit the market. However, larger-screened smartphones are quite popular among users -- the report was rather vague in saying the iPhone test units were just "larger than 4 inches" while the iPad screens were "slightly less than 13 inches diagonally."
The current iPhone, the iPhone 5, is exactly 4-inches diagonally, while the iPad is 9.7-inches in size. Apple's iPad mini, which was introduced last year, is 7.9-inches in size.
One recent report said that Apple was delaying its upcoming model, the iPhone 5S, as it had decided to increase the screen size from 4-inches to 4.3-inches. Most "S" models are minimally changed externally from their predecessors, and most reports say iPhone 5S will sport the same 4-inch screen as the iPhone 5.
However, other reports say that production on both the iPhone 5S and a budget model is ramping up.
While Apple had, until last year, stayed with the same 3.5-inch screen size it introduced in the original iPhone, other manufacturers -- notably, its largest rival, Samsung -- have moved to a variety of screen sizes. Samsung has become the world's largest supplier of cell phones -- not just smartphones -- with that strategy.
That methodology has even created a new segment, the "phablet," which is for phones with screen sizes larger than 5-inches in length. These are seen to be cross-over devices, sitting between a smartphone and tablet.