Sony announced their Xperia Z5 lineup of flagships about three months ago, it includes three smartphones, the regular Xperia Z5 with a 5.2-inch display, a smaller version called Xperia Z5 Compact and the Xperia Z5 Premium, featuring the first 4K display on a smartphone. Sony's Mobile Division has been struggling over time, so it raises the question of whether Sony is thinking on new strategies to attract more consumers into buying their products. The company is currently using a 6-month release cycle for their flagships, so that might be one of the changes in a new strategy.
Another rumor mentioned that five devices would integrate the upcoming Xperia Z6 lineup, a new Xperia Z6 Mini would have a 4-inch screen, the Xperia Z6 and the Xperia Z6 Compact would keep their screen sizes, measuring 5.2 inches and 4.6 inches respectively, there would be a 5.8-inch Xperia Z6 Plus and the Xperia Z Ultra would have a successor with a 6.4-inch display. This rumor might be a little hard to believe as none other Xperia Z lineup has included that many handsets. T-Mobile Poland recently held a press conference and one particular slide (shown below) provides interesting reading. It shows some devices which will be released in the first half of 2016. From Sony, there are two Xperia models launching in Q2 2016. If the timeline is represented accurately, those could be released towards the end of the second quarter, which means around June. Unfortunately, the slide doesn't provide specific model numbers for the two handsets, so there's no way of knowing if these will be part of the Xperia Z6 series. This doesn't quite contradict the previous rumor, as those two phones could have been chosen by the carrier from the whole Xperia Z6 lineup.
Sony already scheduled the conference for the CES 2016, but it doesn't seem likely any new phones will be announced at that event. Still, the company could announce the two new phones a little later at the MWC 2016, which will take place not long afterwards. Then again, if those get launched at June, the announcement could be closer to that date. As for the other companies, according to the leaked slide, Samsung will release 4 phones in Q1 2016, Microsoft will release two Lumia phones in that same quarter and HTC will launch the One A9 and another device, as well, while LG will release four handsets in Q2 2016.