As more and more smartphones seem to resemble tablets, Japan's Sony has joined in by announcing its supersized Xperia Z Ultra phone with a 6.4-inch screen.

The LTE/4G-capable Ultra slips into Sony's offerings between its Xperia Z smartphone announced earlier this year and its Xperia Z Tablet.

Sony has made the leap because the mobile industry has seen "increasing consumer demand for larger screens," Pierre Perron, president of Sony Mobile Comms for northwest Europe, told TechCrunch. "The big screen segment is one of the fastest growing segments."

An obvious competitor in the "phablet" arena is Samsung with its Galaxy Note devices.

The waterproof and dustproof Xperia Z Ultra is powered by a Qualcomm Snapdragon 800 2.2GHz quad-core chip, displaying its output on a 1080p HD display.

For those who baulk at holding such a large device to their ears, Sony will be offering a Bluetooth handset for taking calls, so the Ultra can stay on the tabletop and still operate as a phone.

While saying the Xperia Ultra Z would launch "later this year," Sony did not discuss pricing.