[Miscellaneous Android Development] Pr0xiMUS:
Since I didn't find much information in English about this phone, I'm posting this guide for this great device.

There are 3 versions of device:

CN - Chinese version (4 GB)

ROW - International (European?) version (4 GB)

ROW 8G - International (European?) version with 8 GB internal memory

If you bought it online from Chinese website (like I did - from to2c.com) then you for sure have "CN" version. If you have a device which came stock with ROW firmware, there is no need to flash new firmware because you are already on international version of the phone and you get the updates over-the-air.

Those phones that came from Chinese sites usually have rooted and multilanguage firmware, but basically it is slightly modified Chinese firmware with Chinese apps still included, Chinese GPS settings, OTA disabled (so you don't loose root and multilanguage ((MoreLocale2)) by OTA update) and old firmware. In this guide I'll post how to change the CN firmware to ROW but keeping the CN modem.img because it isn't compatible across different versions of device. Most of the information I've got from site lenovo-forums.ru.

Why doing this? To get...

latest version of non-Chinese firmware (v S120 ROW)

latest modem from Lenovo VIBE ROM (V52)

CWM recovery

root

GUIDE

Disclaimer: you are doing this at your own risk. Some knowledge and previous experience with flashing MTK devices is highly recommended. If you find something confusing in this guide, then you should probably first learn more about MTK flashing and Android phones in general (hint: google :)).

1. TOOLS

- SP_Flash_Tool_v3.1332.0.187, https://www.mediafire.com/?l26qvmalu6m73lw

- MTK preloader drivers, http://xdaforums.com/showthread.php?t=2180436

2. ROM - version S119 ROW full

- download S820_ROW_S119_130922, (LINK) (login information from http://www.bugmenot.com/view/lenovo-forums.ru)

- flash using SP_Flash_Tool_v3.1332.0.187, make sure that all the files are checked, use firmware upgrade mode as shown in pictures bellow...

3. Flash custom recovery

- get recovery CWM_v6.0.3.4_S820_ROW, download link: https://www.mediafire.com/?82bb42qg55o3ob4 (credits: lenovo-forums.ru)

- flash with SP Flash Tools using Download mode like shown bellow...

4. Flash S120 ROW update (CWM)

- get into recovery by pressing vol down + vol up + power.

- flash this incremental update (S119 -> S120), download: https://www.mediafire.com/?3e11hd2erutsz3k (source lenovo-forums.ru, modified by me because of asert errors in their file)

5. Root device

- enable usb debugging by opening developer menu: Settings -> About -> Versions -> pres 7 times on baseband version

- follow root guide from this link: http://xdaforums.com/showthread.php?t=2247537

6. Change MODEM.IMG to V52 from VIBE ROM

- download this modem.img (V52 from VIBE ROM): https://www.mediafire.com/?au982otib7lkka4

- you flashed international version of firmware (ROW) but modem still have to be from the Chinese ROM to function properly - following guide from this LINK you can swap the MODEM.IMG from ROW version to Chinese (procedure for different phone but works analogously). In short: transfer modem.img to your sdcard, mount /etc/firmware as rw (read/write - you need root rights to do this), copy over existing modem.img, change permissions to 644, reboot phone (pull battery out)

Enjoy the international/EU version of Lenovo S820! :)