In my experience, one finger typing on a touch screen doesn't help muscle memory at all, it's completely different.  I comfortably used Colemak on PC (touch typing) and Qwerty on touch screen in parallel.  That is, until I switched to MessagEase and never looked back. :-)

Sounds interesting... but I believe I agree with ghen; I don't think it works that way in practice.

Splitting up learning processes is nice (cf the Tarmak), but I think the touch screen training will be an ultimately unnecessary and not sufficiently beneficial step. This is just speculation on my part though, and since you feel you had good results with it I'd love to discuss the method further! :)

I was somewhat surprised when I realized I have a very visual knowledge of Colemak myself, possibly due to having made a lot of images of it. Several users who type faster than me appear largely unable to easily see the layout in their head but merely have it in their fingers. This came up in the discussion of my MessagEase modifications which I felt made the layout easier to use and remember.

Actually, using the Colemakoid MessagEase layout could possibly be a middle ground that's both efficient on the phone and helps remembering Colemak positions for the upper and lower rows? The home row isn't helped by it but you can't have everything and I think that using an efficient input method will be more pleasing.

Hmm... well, I always sucked at typing on tiny screens and I would take a real keyboard any day, but I think there is some kind of connection between visual memory of a layout and the ability to use it on a small screen at least.  After all, you pretty much have to look at it to use it anyway, so having a visual map in memory and knowing the general location of each key is pretty important.  Not so sure about the benefit of learning on a real keyboard though, since muscle memory rules supreme there.

I can say, however, that as I progressively got better at typing with Dvorak and began to slowly forget the QWERTY layout, I was in for a surprise when I tried to enter text on my phone again.  I was effectively no longer able to use Swype at all hardly!  I think my ability to use QWERTY on the real keyboard probably diminished before my ability to type it on the little screen, though.

Still, I decided to take the advice of other users on this forum and give MessagEase a try, and I won't be going back.  For entering text on a touchscreen, IMO it's a must... QWERTY, Dvorak and Colemak are all a joke in that case.  Trying to cram a full-size physical keyboard layout into a small touchscreen has to be up there with some of the dumbest ideas ever, and strikes me as quite lazy and unimaginative.  No wonder innovation in general tends to be so poor at times when people come up with ideas like this to get on the market instead of doing proper research for new potential methods that are better suited to the device and/or task at hand.