Yole Developpement publishes an article on mobile phone camera trends. Few quotes:
"First, it seems that in the recent years Apple has slowed down its innovation drive on the camera side, so competitors have been able to move ahead. This is the case for the dual camera setup on the rear side of the phones.
Second, the importance of biometry has had a direct impact on cameras, which are now potential biometric devices. Samsung has implemented a second front-side camera, in the same way Fujitsu had experimented with less than a year ago, in order to provide state of the art iris-recognition technology.
Third, the usage of the front camera is evolving quickly. We had mentioned in our CMOS Image Sensor report the selfie trend’s impact on front facing camera resolution. Companies like Oppo are surfing this wave by improving the performance of the front camera, and recently providing a dual front setup for the F3."