After only two years .Mobi broke the 1 million mark. Sites such as Nokia.mobi, Mercedes-Benz.mobi, Zagat.mobi and Bank of
America’s BofA.mobi have been successfully promoted as custom,
intuitive experiences for their users.

I am not really surprised about the success of .mobi, but I am not sure if the mobile web really  needs its own domain. A subdomain should be sufficient, especially that domain grabbers took a lot of good domains and big web brands don’t own the mobile version.

The approach m.domain.com is probably one of the better solutions over the long run.
However check the post about mobile domains a few days earlier