Please add anything you know in the comments, and I will keep the OP updated with the latest information.
What we know so far:
A list of stock firmwares is maintained in this thread:
You can flash D6503 Roms on docomo SO-03F, but some features are disabled. Specifically:
- docomo features
- TV related features
- NFC (includes FeliCa, Osaifu-Keitai)
When you want to flash D6503 FTF on SO-03F, be careful to partition.
You'll get only 16GB storage if you didn't exclude partition because SO-03F has 32GB but D6503 has only 16GB
On Unlocking bootloader/rooting:
All Japanese Xperia models can't unlock bootloader, Japanese Carrier Model is locked bootloder.
Go to DOCOMO store and open up the phone and type in *#*#7378423#*#* and check if the bootloader can be unlocked.
Phone should be locked to DOCOMO, you need to pay a small fee to get it unlocked. You need to make at least one call on an active DOCOMO SIM to complete the SIM unlock.
The SO-03F supports the following bands:
- LTE 2100/1800/1500/800 MHz (Band 1,3,21,19)
- WCDMA 2100/850/800 MHz
- GSM 850/1900 MHz
(The docomo site seems to only list the 4G bands)
Full specs can be found on the docomo site:
Wiki, including rooting guide (in Japanese):
Translation of the rooting guide from the above link:
!!!If any of the links fail, please visit the original site and try them there!!!!
D6503 can be rooted, so SO-03F can also be rooted.
SO-03F 17.1.B.0.318 root method
Things you will need:
1. Root as detailed in this page
2. Unzip Z2-lockeddualrecovery2.7.***-BETA.installer.zip and run install.bat to install the recovery
3. Reboot, and when the LED comes on push the volume key, enter recovery, and install the SuperSU zip
While it should be handled by rootkitXperia, should you be unable to remount system in RW mode, install this zip from recovery.
When updating to a version that cannot be rooted by rootkitXperia, if you want to maintain your root you must update using a prerooted .zip
A custom recovery is necessary for this, so please install XZDR etc. in preparation.
Newest Flashtool (Mirror)
.zip to run with ric_disabler in install-recovery-2.sh
1. prepare prerooted zip
Open PRFCreator, create prerooted zip
Details of this difficult process are in this article
2. Enable USB debugging
3. Connect to a PC, copy flashable.zip to the phone
(you can name it anything you like)
4. Reboot and push the volume key, start CWM / TWRP, install flashable.zip
5. Install sony_ric_disablerv2_signed.zip