[Sony Xperia Miro, Tipo (Dual), J, E] jjm34:
Installation (unlocked boot loader required):

If you don't have stock JB installed (11.3.A.2.1), you need to flash that first because this ROM only works with the baseband firmware that gets flashed with the stock JB ROM. GSM will be unavailable if you're coming from ICS.

Flash a recovery if you don't have one, e.g. CWM, or the boot.img (TWRP) included in the ROM's .zip.

Boot to recovery and...

Wipe data+caches

Install the ROM .zip

Optionally install GApps

Backup instructions not included because you should be smart enough to do that yourself.

Current releases:

Xperia E single

Xperia E dual

Other files, including incremental updates from previous releases

Multi-SIM operation:

Enable/disable SIM cards in Settings / Multi-SIM.

Only one SIM card can have 3G enabled, but it's not toggled automatically. To enable 3G on one SIM you have to make sure the other one is set to 2G-only mode first.

Some of the dual-SIM features in Sony's ROM, such as auto-toggling SIM cards based on time, different ringtones, or data usage tracking aren't included.

SMS are currently always sent from whatever subscription is set as the SMS send subscription. This includes sending an SMS reply from the "incoming call" screen or the "missed call" notification.

Note that battery life is shorter when two SIM cards are enabled. The reason for this is that the modem has to keep switching between two networks to remain registered and be able to receive network events, causing higher power consumption, higher latency, and lower throughput. This also causes the data connection to become slower when two SIMs are enabled. This isn't something that can be "fixed" because it's not software-related. Having only one SIM card enabled will improve battery life and data connection speed.

Kernel:

The inluded kernel is based on Sony's sources, so no additional governors, schedulers, etc.

Sources on GitHub.

USB mass storage mode:

I have enabled the USB mass storage driver to support mounting two storage devices simultaneously, so you can share both the "internal" and "external" SD cards as UMS.

Recovery will always mount both storage devices, but the Android GUI for USB mass storage will share the external SD card only, because the internal SD card is intended to remain available to the OS. However, you can manually mount the internal SD card from the shell:

Unmount storage from the OS:

vdc volume unmount sdcard

To unmount forcibly:

vdc volume unmount sdcard force

Share to USB:

vdc volume share sdcard ums

To disconnect from USB and re-mount storage to the OS:

vdc volume unshare sdcard ums
vdc volume mount sdcard

Known issues:

Video recording doesn't work

Video playback uses software decoders, not hardware

Magnetometer doesn't seem to be working

USB mass storage speed is slow

FM radio not included (hardware and driver work, and tuning works as well, but it's going to require quite a few changes to the audio subsystem to actually get sound out of it)

Turning off screen in recovery doesn't work (screen timeout disabled by default)

Inserting an unmountable SD card (unformatted, or unknown file system) will trigger a notification offering to format it. However, doing so will format the internal SD card

A data connection disabled due to roaming might not re-enable when switching back to the home network (Workaround: toggle airplane mode on/off)

Enabling ADB over network disables charger/USB detection

What I haven't tested:

Emergency calls. I assume these will work because generic telephony works, but especially in the cases of the phone not registered on a network, or calling without a SIM or a PIN-locked SIM, I really can't say (and I don't plan on calling up emergency services just for testing purposes). If anyone tests this, please post your results.

Third-party telephony/messaging apps (Dialers, SMS, etc.). Those might only work with whatever SIM is set as the default.

Bluetooth headset

MMS

RUIM card operation

CM's SMS limiter (Settings / Security)

All of my sources are on GitHub, and should be used with a manifest file to download the code base.

Credits:

CM devs for CM10, FXP for device bringup, TeamWin for TWRP, Code Aurora for the multi-SIM implementation.