At this point, Sony's Xperia Z4 may already be one of those smartphones that have overstayed in the rumor mills. Word about the flagship has been out since 2014, until speculations claimed its arrival in January's International Consumer Electronics Show (Las Vegas). Unfortunately, no public launch ever happened.

Few weeks later, the device has been pegged to appear at the Barcelona-based Mobile World Congress, beside the Samsung Galaxy S6 and HTC One M9. To fans' dismay, there were still no signs of the anticipated smartphone, but Sony nevertheless revealed an Xperia Z4 Tablet.

That may be enough for a consolation, but until the Japanese tech giant confirms, we can never really tell how close this tablet is to the handset.

Interestingly, recent reports seem to be more favorable. Last week, an unidentified Sony handset passed the Federal Communications Commission's testing procedures, dubbed under the code name PM-0780.

Supporting a wide range of LTE bands, the device is noted to have six different variants, all identical in hardware. Its width and height dimensions, moreover, are similar to the Xperia Z3's (5.75 x 2.87 inches).

Its battery is said to be non-removable, but it appears to possess a microSD slot -- something the recent Galaxy S6 models missed.

Today, a new report suggests that another Xperia device is in the works, GSMArena reported. This is assumed to be the Xperia Z4 Ultra.

As cited by the outlet, the Ultra is seen to succeed 2013's Xperia Z Ultra. At the time, the latter is thought to be "the best phone you'll probably never buy," Engadget reviewed. For a measurement of 179.4 x 92.2 x 6.5 mm (7.06 x 3.63 x 0.26 inches), the outlet concluded that it's "awkward to hold."

In a separate preliminary specs sheet, GSMArena listed the Xperia Z4 Ultra's screen at 6.44 inches. It's allegedly powered by Qualcomm's Snapdragon 810 processor, 3 GB of RAM and a non-removable 4,000 mAh battery. As indicated in the outlet, the device is expected to release in Q2, and by any chance, today until June would be a viable time frame.

The device is expected to hold an IP68 certification, which means it's dust-proof and water resistant at a depth of 1 meter, submerged in 30 minutes.

Other purported specs include a resolution of 1080 x 1920 pixels, Triluminos display, 16 and 32 GB storage options, 16 MP main camera and Android 5.0 Lollipop support.

On the other end of the rumor mills, TechnoBuffalo cited specs such as QHD display, 4 GB of RAM and a stylus.

The standard Xperia Z4, nevertheless, continues to make rounds over the headlines, following an alleged camera shot that highlighted its 20.7 MP sensor. As told by TechRadar, the image appears to have been taken at the Northumberland National Park, England. The device is speculated to sell for $1,250.