Apple has been testing larger screens on their iPhone and iPad devices, the tech giant's supplier told the Wall Street Journal.

The iPhone screens tested have been larger than four inches, the size of the current iPhone 5 and iPad screen sizes tested were 13 inches diagonally, sources said.

Whether these changes will stick is not certain, as Apple often tests different designs leading up to a product's release. The testing appears to signal that the smartphone maker is attempting to diversify their product line with devices of different sizes and capabilities.

In April, the Journal reported that the Taiwan supplier said Apple was considering offering a nonmetal casing and a choice of five or six different shell colors. That report was unconfirmed, as is this one, but the Cupertino, Calif. company may be trying to assimilate to its biggest competitor, Samsung.

Samsung has overtaken Apple as the world's leading smartphone maker by offering phones in different sizes.

In the first quarter, Samsung lead the market with 33.1 percent of the market while Apple took second place with 17.9 percent. Apple still leads the tablet market with 39.6 percent, however, that number has fallen since it was 58.1 percent last year.

"In the long run, we will see touch screens in all sizes as the future vision of the technology industry is to offer the same user experience across all screens," said IDC analyst Helen Chiang. "The key is to bring down the cost and introduce compelling applications for large-screen devices."

Samsung, Sony and Huwei have all released smartphones with screens larger than five inches, creating the "phablet" (phone + tablet) category. Phablets are phones with screens too large to be considered just that. Their large screens are a tablet characteristic, but calling ability still makes them phones.

The iPad is currently 9.7 inches diagonally and the stripped down version, the iPad Mini, is 7.9 inches. A 13-inch display would make the tablet about the size of a notebook.