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

Interesting post over at EverthingUX regarding what URL to pick for mobile usage. I have heard a lot and a lot of different approaches. However I personally think that there is no right or wrong. Some URLs are just too long to work for mobile, others are not. Some websites should probably rebrand for the mobile web, others are fine with an .mobi extension.
And yes…the Key stroke. Can we really now say that the Keystroke is still important?

Who knows? Below Everything UXs approach:

.mobi
Pros:

• It’s short and sweet and dodges the whole .com, .es, .org confusion.
• It’s pronounceable

Cons:

• It’s not a proper word, and what’s to stop people trying .mob, or .mobile?

.mobile
Pros:

• It’s a proper word so easy to spell AND pronounceable

Cons:

• It’s longer than average (com, net etc) so takes longer to type, -but at least predictive text could guess it.
• Maybe
  Americans would want to type .cell and native speakers of every other
  language their own cultural or linguistic equivalent.

www.m.
Pros:

• It’s slick and sexy, very web 2.0.
• It’s short

Cons:

• It
  adds another full stop to the url, which can be a pain to type (did I
  type a full stop or a comma? where was the punctuation button again?)
• It can also increase cognitive load and confusion: Do I need to type the www. like in the old days? Did the “m” go before or after the “www.”?

Same url for desktop and mobile sites
Pros:

• The computer does the hard work. You connect from a mobile device, the page adapts accordingly.
• No extra memorising required on the part of the user.
• Greater confidence and security that the site really is the site in question, reduced concerns about phishing.

Cons:

• Doubts about whether the page you’re viewing has been adapted for mobile device. Is all the content here?
• There may be a delay in detecting the correct version (language, device etc)
• Takes
  away choice from the user; it’s likely that the user will sometimes
  want to read something they saw earlier that day at work for example.

.com/mobile
Pros:

• Intuitive,
  matches the model of pretty urls considered best practice, although
  it’s not strictly the same (it’s more of a microsite than a page)

Cons:

• The length
• Still have to remember the site’s domain
• Another forward slash