Personally, I use only MobileGTD. I got quite fast typing with T9 and love to walk around or lie down while processing my projects.
I've had a quick look at org-mode, but it has much more functionality and therefore a much more sophisticated file structure than MobileGTD...
It might be possible to read a subset of org-mode, but I don't have the time to implement this.
If you want to try I can grant you access to subversion.
Regards
Martin