I have been using I phone 6 s 64gb for the past 1.5 years. it has been nice. the voice quality is nice. you can clearly hear the sound without any discomfort. the sound quality of the speakerphone is good. but the sound is not loud. I have not faced any hanging problem with the phone till now except only once the phone while updated hanged for 2 hours. but the patience is needed and it self resolved. the camera quality is very good. thought it lacks a optical image stabilizer. the battery back up is ok. in standby mode the battery lasts for more than a day with moderate use. heavy use will drain the battery fast . so will need to carry a backup for power.front camera is good. personally I have been using facetime which provides very good quality of video and audio call via internet. It has a very fast fingerprint sensor which is integrated in many ios apps in the phone for added security.
initially android users will feel that the phone is very restrictive but with use it becomes very easy to use. the integration between apps is very good and that makes day to day working a breeze