The importance/relevance of top level domain names for mobile has come up recently in a few discussions with peers who are building mobile websites. I've been asked quite a few times if I thought it was important for someone launching a mobile site to purchase a .mobi domain for their site. I've given this a lot of thought lately and have discussed the benefits of having specific domain names for a mobile site with colleagues and have come to form the following opinion about domain names in regard to mobile sites:
The domain name of your mobile site is only relevant insomuch that it is relevant to mobile search engines. So the top level domain (i.e. .com, .net, .mobi) probably doesn't make a whole lot of difference.
Here's my argument; domain names are not a good way of addressing content. Entering a domain name into your desktop browser is an easy thing to do, and if you are not sure of the spelling or can't remember the address perfectly, it's no big deal to try until you get it right. Companies like Marchex are making bank on the fact that some people will just type in www.
So if the mechanism for finding information/content on a mobile browser is search, you need to be making sure your content is relevant, not your top level domain. While the mobile search engines do give weight to the words that appear in your domain name, it's apparent that they do not discriminate based on top level domains. Why would they. Having a .mobi TLD does not ensure that the content is mobile content, just look at http://pc.mtld.mobi . No, the way they determine the content type of your site is by looking at the doctype of your page. So if TLDs are irrelevant to the mobile search engines, the primary user interface for finding content, you are just as well off with a $.99 .info domain from GoDaddy as you are with the $18.99 .mobi domain for your mobile site.