We looked at the options a few years ago and decided to go in
another direction, so my memory might be old.
The actual domain is .MOBI It is intended for developers who
want to develop applications for Mobile devices, and allow end
users to ensure that they are viewing the mobile version, as
opposed to the "desktop version" of a website.
The advantage, as best I can tell, would be one of perception
on the part of the end user. As for real benefit, it is lost on me.
My thought process would be to attempt what I suggested
above, and make use of different style sheets depending on the
information you can retrieve. If you can't retrieve ANY information
that leads you to believe that this is a mobile device, the, make
an obvious link that ASKS the end user if they want to use the
mobile version of your site.
Theory vs. Practice are often much different, though. The
complexity of your site will likely dictate your path. If you
ultimately determine that it is easier to develop a completely new
site specifically for mobile users, you can auto forward mobile
users to the MOBI domain, and therefore not have to "market" both
your COM and your MOBI domain. If a mobile user happens upon your
COM domain he will not be tunred off by the fact that it is not
optimized for his three inch screen, since he will be auto
forwarded to the MOBI site.