The aim of the review is to help the searching people by providing accurate info, I have tried it as a token of gratitude to contributing netgens, since I am taking regular info from net , though I am having very limited time to contribute.The phone is having FunOS. it is comparable to any launcher over android OS. It is customized to meet the requirements and to give a wonderful user experience. It's Dialer is Ok , Messages is having additional facility of sending Vcard as an attachment / text (better than old Nokia facility), The icons are beautiful, pleasant &legible. Colour combinations of icons over black wallpaper are excellent. It is having iManager, which is powerful enough to speed up / clean RAM and close any installed apps. It is having useful facility of white list, so that it will not kill the apps included in the white list. Hence you may not need any rooting of the phone at all. It is having only 1GB RAM, but no lag at all. Alarm tone is nature's sound & very pleasant. Ring tones are excellent. Selectable HiFi mode. Cameras, both rear & front are good. Good signal catching. Ring tone volume is OK (at maximum level). Probably Vivo made so many customizations / refinements, it takes lot of efforts & time to bring new versions like kitkat,lollipop etc with the same excellent user interface.Android app short cuts are installed on screen like IOS, hence no app button in latest Firmware version. Settings are similar to IOS (these are the changes with respect to stock) . But it is fully compatible Android. Probably they have aimed at IOS like user experience with android flexibility.When it comes to audio quality, most of the phones fail to impress audiophile & initially many of the users may not pay attention to audio quality. So I have compared (At EQUIVALENT VOLUMES for both RMAA & subjective listening) the Audio quality of Vivo X3S to many phones like Iphone 4 (It was reference to any phone in audio quality with flat frequency response, low noise & IMD, very low output impedance in the range of 1ohm, excellent stereo cross talk etc) , Iphone 4S, Nokia E52, Samsung A3, Samsung S III & USB sound card FIIO E07, probably VivoX3S is one of the best phone for bundled IEM / 16 ohm impedance ear phones/ IEMs in audiophile point of view [The frequency response is not as flat as iphone4,but the difference is negligible (+0.3db)]. However FIIO E07 with any android phone (with OTG) or PC (USB) tops the list and beats Iphone 4 in every parameter. Even veteran Nokia E52 performs very well, far better than iphone 4 (at equal Volume level) except in Stereo Cross talk. Vivo X3S supports native 44.1 kHz playback which is also important for music fidelity. It may be noted, HiFi is available only headphone mode. In fact non HiFi mode is also fared reasonably well. The phone is bundled with excellent 16 ohm impedance IEM/Earphone; you may not need to purchase any additional IEM/ earphone / headphone. However if you are purchasing a phone with music listening as an important parameter, please have a demo before the decision (it is applicable to any audio device). The latest / costliest need not be the best e.g as on date, many latest phones have native sampling frequency support for 48kHz not for 44.1 kHz.Surprisingly all features of X3S are excellent except few limitations given below.However I have few reasons to root the phone.1) Though it supports OTG, FIIO E07 was not working, as USB storage is implemented at another level. However this can be fixed by app USB Host Check if rooted. (the music quality of X3S is so high, anything better may be beyond human hearing capacity or atleast negligible, so FIIO E07 may not be needed or unnecessary bulky)2) FunOS is desig is wonderful,still one common option of change of font size is missing, though the existing font size is OK, this can be fixed with BigFont app but it needs rooting (I want larger size font to compensate my eye sight, which is at the manageable level).3) The In call volume level is normal at maximum setting, but I want little bit higher volume like Moto G or Razr M, so i want to explore any possibility to increase the gain through rooting. (Call Volume Booster app may used to keep in call volume to max in auto, at the time of calling/call receiving)4) Messages is in conversation mode (like all others android phones, inbox / sent /outbox/draft/custom folder are not available, however Pansi SMS can be used but up to Android-KitKat version as the developer stopped the development, as on date)Other Limitations / deficiencies.1) Clipping at 0000% is occurring (0000% has no meaning, but error message is appearing) during RMAA, even if specified line in / volume levels are set to calibrated value,2) It accepts 16 ohm impedance IEM / load very well (But at 32 ohm impedance load, frequency response etc were lower than 16 ohms, whereas the sound performance of other phones was better with higher impedance loads).3) Notification LED is not multi color (only green)4) The length of the phone is high at 143 mm (it is higher side for even for 5" screen), I prefer phone length of less than 130 mm, but No HiFi model is available with the lower length.5) FM Radio sensitivity is poor compared to MotoG but approximately equivalent to Nokia E52. Very poor compared to stand alone radio.I am happy to say that I am unable to find any other deficiency in the phone as the date of review.Downgrading & Rooting Vivo X3SIt is shipped with firmware version PD1227BW_EX_A_2.7.0 which is not rootable with any of the available tools like kingoroot-1.3.9, RootGenius_1.8.7, Iroot v1.8.5. Hence the following method used to downgrade & root. The following is the experience sharing for Vivo X3S only (please do not be confused with Vivo Xplay 3s, it is a different model), you are responsible for your actions. Never ever flash / update the ROM not meant for that phone (i.e. make, model, model-variation etc are to be same)Downgrade1. Put Zip package firmware version PD1227BW_EX_A_1.24.7 in phone internal storage (IMPORTANT).[at present PD1227BW_EX_A_1.24.7 or lower version are rootable)-Firmware can be downloaded fromhttp://www.vivoglobal.com/download/5.html2. Enter recovery.Entering the recovery mode:- Turn off your phone.- Hold and press the volume up key + power key together about 10 second.- Use volume keys to shift "selection" on to Recovery Mode.- Press Power key to enter the Recovery Mode.3) Use volume keys to shift "selection" on to Wipe data/factory reset & press power button , now shift "selection" to user data.... '.yes again through volume keys & press power button.4) Use volume keys to shift "selection" on to Select Wipe Cache & press power button5. Use volume keys to shift "selection" on to Apply update from internal SDCard & press power key to select it , now select your zip package , depends where you put it.6. Wait patiently till setup is complete.ROOTINGCAUTION & RISKS INVOLVED:i. The built in counter of phone permanently records rooting info, even if you un-root it, this will not reset. Hence warranty may be void. In view of this, rooting may not be advisable, atleast before reliability of hardware is established. As the risk lies with user (advanced & willing) & not with m/s Vivo, it is a win-win situation, as the Vivo is not locking the OS, like IOS or boot locked Andoid by Moto. Further the above downgrade method works only if phone enters into recover mode hence may not be suitable to bring back the bricked phone(which may need different flashing method, which is not known at present). In view of this & Vivo has done many useful tweaks, rooting may not be required at all.ii. Even if you rooted the phone, never delete or even edit any system file or to that extent any file (even if you have right tools & knowledge, if not executed properly the phone may not boot after next restart).iii. If you select 'allow' out of allow / deny for any program, when asks for root permission on your rooted phone,c it means, you are giving administrative rights to that program.1) Install USB drivers "All MTK USB Driver 2014 " on Windows PC (may be googled to download)2) download and install any one of rooting tools like kingoroot-1.3. or RootGenius_1.8.or Iroot v1.8.5 (I have used Iroot) (may be googled to download) on Windows PC.3) open the application in PC & connect the Vivo X3S to PC through USB cable , now on the debugging mode on phone ( unlike other android phones, this option may not be available before connecting to PC. However full developer mode can be accessible by dialing * # * # 7777 # * # *)4) Click on root & wait (Un-root option is also available at options of app) Phone will be rooted condition, may be checked with root checker.