It works for some and doesn't work and brick the phone for others.
In one of the threads I posted results of my testing.
I was able to restore my GB nand from ICS and than restored ICS nand from GB.
Worked without any problems or hick ups. But I don't know if this is exception or the rule.
Like some get GPS lock and message indicators, and some don't, of which I'm in that category.
Wanna try to avoid the Bricklay'n category
As of now, I want to reinstall FC07 ROM, FC07 Modem (maybe) and Repacked Kernel FC07 w/CWM.
I'm on FC14 ROM w/stock Kernel and FC15 Modem.
I'm gonna >
1) Install ODIN 1 click EL29 Convenience Pack w/CWM from sfhub
2) Lock onto GPS
3) Boot into Recovery w/GPS locked
3) 'Format All' by Calkulin *
4) Flash FC07 ROM .zip
5) Maybe the FC07 Modem in same session
7) ODIN FC07 Kernel/Recovery w/CWM by Steady Hawkin
Update after EL29 One Click w/CWM install
1) The one click was great Thanks sfhub!
2) reinstalled FC07 ROM and Modem
3) I finally have GPS! (9 Sats In View, and in Use)
But the GPS circle indicator remains in the upper tray, even though I turned off GPS.
I have to reboot to get rid of it.
Update: Fixed itself
4) Gonna install FC07 Repack w/CWM
One issue that still remains >
1) Pinch Zoom flow does fit screen. I have to still scroll horizontally to view entire text.
Double tap zooms and fits screen, But zooming any larger does not flow to fit screen.
The above worked when I was in GB EL29 for 10 minutes.
Al least I have GPS.
* I didn't 'Format All' when I flashed FC07. I thought I might lose the GPS lock during the flash.
I now have Pinch-Zoom Reflow again.
I installed Opera Mobile 12.0.1, which gave me back the capability.
Stock Browser and Dolphin HD Browser's Pinch-Zoom Reflow didn't work on ICS Roms.
The above was my experience, and ymmv.j