OK Guys ... finally managed to get my Mozart updated to NoDo.
Used the intructions from here (lots of unsuccessful reports for Mozart apparently)
Lots of users also reporting success over on the Omnia forums with some more giving some handy tips
I only used the first link & followed it precisely.
Also before making the first VPN connection I flushed the DNS cache on my laptop to remove stale entries (from command line type "ipconfig /flushdns")
Also when Zune presents the update and you get to "Step 2", you need to disconnect the VPN connection and browse to google on a browser otherwise it just sits at 0% and fails (because it has the VPN gateway metric sitting in your PC's route table with a lower value than your proper default gateway).
1st Attempt failed.
2nd Attempt found the update and failed because Zune stopped responding and crashed (because I disconnected VPN too early ... before "Step 2" on Zune)
3rd attempt Success and kept ALL my settings
For the sake of making it quicker (whole process took 45 mins for me) remove all media (mp3 & Videos etc) from your phone or your backup stage (on Zune) will take that much longer.
HTC Mozart (Unbranded & Sim Unlocked)
Rom - Trialing Various. Current = DFT v2
OS = 7.0.7720.68
Firmware = 2250.21.40600.401
ROM - Dutty Creme V10 (WinMo 6.5)
Radio - 188.8.131.52
HSPL - Bepe & Cotulla 1.42
Rom - Orange 184.108.40.206 (Official)
SPL - 1.40.OliNex
Radio - 220.127.116.11
Rom - Gen.Y-D2_R3_WWE