We can already differentiate services by using a prefix to the domain name: compare http://www.futureplatforms.com and wap.futureplatforms.com; you don’t need a new domain name to do this.
Saying a service is “mobile” doesn’t tell you anything about which “version” of mobile it is: WAP? XHTML? cHTML? If you plan to automatically determine which version you’re going to deliver, that’s great: but in this case you don’t need a separate domain name. Just hand out “futureplatforms.com” and redirect as necessary.
There’s an underlying assumption that URLs are relevant to everyday users of mobile services – that in a few years time, we’ll all be tapping addresses into our handsets to access sites. Personally, I don’t like this: the reach of mobile goes way beyond the reach of the fixed-line internet. People who don’t know or care about underlying technology use mobiles every day of their life, and it seems rather arrogant of us (mobile service providers) to expect them to learn about browsers, servers, sites, and URLs in order to get them to spend time and money with us. The mobile internet needs to be easier than the web, rather than apeing (sp?) it on a small screen. Just because the people building the mobile Internet understand URLs doesn’t mean that users have to.