As far as I know, current smartphones and "smart" tablets (e.g.
android/ipad/meego/playbook) all use NAND flash memory for storing the
OS. I believe the reason your iphone boots so quickly is because you
are just waking it from a sleep state. You either have to let the
battery die completely or else hold down the power and "home" buttons
to actually get it to reboot. On the iphone 3g that I have, boot time
is around 30-40 seconds if I actually reboot it. If you are looking
for instant-on linux, you can check out the webtop OS Asus offers on
its current laptops (also any of the other various "webtop" instant
OSes that come with different laptops- their all unix-based).

For installing something, have a look at mandrivas instant on os,
though it is not free:
http://www.mandriva.com/en/instanton/

There is also a thread on the net somewhere for building a five second
bootable xandros or Arch Linux. Also, I have been told that Ubuntu
10.04 and up is supposed to boot in 10-15 seconds with sdd drives,
though on my old disk with ext3 formating, it's around 50 seconds.

There are several Linux based Portable Tablet Computers running on
Android available now and all are instant on. The foremost is the
Motorola Xoom. It got the best of show award in January
ces.cnet.com/motorola-xoom-wins-best-of-show. I'm just about to
purchase one and I'll probably post my impressions in a few days.

Specs: 10.1 capacitive touch screen; stereo speakers; front (2 MP) and
rear (5 MP) camers; 32 GB built in flash memory; 1 GB RAM; 1 GHz dual
core CPU; access to the full Android Marketplace and apparently even
the phone size apps work well and don't look too bad; a hundred or so
Tablet specific apps and growing rapidly. I'm getting the WiFi only
version and will tether to my Dell Streak when necessary, but I don't
anticipate using it "on the run" much.

The sheer quantity of files that need to be run to create an OS
basically. Using an SSD and hibernating instead of shutting down is
about as close to 'instant on' that a full OS can get to currently,
but even so it would need a full close down and restart for some
updates. As hardware speeds increase the speeds of even a full OS boot
will get short enough to be as close to instant on as makes no
difference :-)

Smartphones / iPads etc are not full OS's, they have a very restricted
operating system compared to an installation of Windows / Linux / Mac
etc.

Thus my constant cry for someone to write a new 21st Century Internet ready OS
completely in Forth. Chuck Moore, where are you when we need you.

Chuck is still there and about to make a splash it would seem from
this... www.greenarraychips.com/home/about/index.html !!

Thanks for the link. Can you maybe send me your assessment of Chucks Array Chip
multicomputer thingy off line since it may not be of interest here.