The Sony Xperia Z4 is one of the less likely announcements expected to be seen at the MWC a few weeks from now. But there isn't anything spectacular. It looks about the same as the one on the Xperia Z3. The front cam and light sensor positions have been reversed for some reason, but that's all there's to it.
There are two things we felt like they are safe to say. The first is that this unassuming panel will look as great as it always did when it's joined by the glass cover and finely sculpted metal frame. Although the bezels look quite thin, they might end up looking a little thicker in practice, due to the way the frame covers them a little bit - look at the Xperia Z3's front panel to get what we mean.
In a move away from the Xperia Z3 and back to the Xperia Z2 the speakers have been repositioned behind thin slits at the edges of the panel. HTC One (M9) was recently revealed to sport a similar design.
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We expect to see more from the Sony Xperia Z4 as the months ahead of its second or third quarter announcement dwindle. Specs wise, it should be a Snapdragon 810-powered beast with either 3GB or 4GB of RAM, and possibly two 1080p/1440p display resolution variants.