You must have:

 - phablet repo
 - Samsung Galaxy S GT-I9000 running CyanogenMod 10 or 10.1 with CWM.
 - Backup of /efs (if you don't know what this is or why you need it, stop reading this guide NOW.)

Add these lines in .repo/manifests/default.xml:

  <project path="device/samsung/galaxysmtd" name="CyanogenMod/android_device_samsung_galaxysmtd" remote="github" revision="refs/heads/cm-10.1" />
  <project path="kernel/samsung/aries" name="ali1234/android_kernel_samsung_aries" remote="github" revision="refs/heads/ubuntu-touch" />
  <project path="device/samsung/aries-common" name="ali1234/android_device_samsung_aries-common" remote="github" revision="refs/heads/ubuntu-touch" />
  <project path="hardware/samsung" name="ali1234/android_hardware_samsung" remote="github" revision="refs/heads/ubuntu-touch" />

Commit changes:

cd .repo/manifests/
git commit -a

Fetch new repos:

cd ../..
repo sync

Get binaries from phone (plug in phone running cyanogenmod 10.1 first):

cd device/samsung/galaxysmtd
./extract_files.sh

Build it:

cd ../../..
brunch galaxysmtd


Now you'll have a zipfile like cyanogenmod-xxx-UNOFFICIAL.zip. Transfer this to your phone, and also transfer the quantal-preinstalled-phablet-armhf.zip. 


My build is here:
Mirror 1: http://ubuntuone.com/0aGhALmE950fNzSn5Tp8vg
Mirror 2: https://docs.google.com/file/d/0B2am7h6Tso0TVGo0M1dWMHBkZXc/edit?usp=sharing


Boot to recovery (CWM).

Select to flash from SD card and flash the cyanogenmod zip first. 
Then format /data. IF YOU DON'T DO THIS IT WON'T WORK.
Finally select to flash quantal-preinstalled-phablet-armhf.zip from SD card. 

Reboot phone and wait for Ubuntu Touch to appear.

UI will be too big. You need to edit /usr/bin/ubuntu-session to change screen DPI variables. 10 and 1.0 work fairly well.

For me: WIFI works, camera works, audio untested, calling untested. Phone gets very hot, and apps load slowly, but once they are loaded they are fast.