Nice idea. Except, there are probably alternative methods of achieving the same result. It was no coincidence that I used the verb 'fingered' above. Back in the good old days of the Internet the Finger protocol essentially did the same thing. Is anyone still using Finger?
I'd also question why I'd need to register an iTAGG mobile domain name to get this kind of functionality. For a start this is a proprietary commercial service. Are iTAGG's mobile domain names likely to achieve proper domain name status? Well we'll see but don't count on it. Also, I already have a unique mobile domain name. I call it my mobile number. The nice thing about my mobile number is that there are already well-established mechanisms to ensure that my number is unique. Although iTAGG will guarantee you a unique 'domain name', rival companies (if they ever emerge) will be under no obligation to adopt an interoperable naming convention. Sure, iTAGG domain names are easier to remember than numbers, right? Maybe. Once all the cool and obvious names have been registered you'll be stuck with the Hotmail username scenario (yes, I'll probably end up being david-davies834. And not to mention that you'll also have to remember iTAGG's short access number to make the system work at all. So with iTAGG you'll have to remember both my domain name and the access number.
iTAGG have a nice idea and I'm sure many will use it. However, as smart phones get more popular then why not use that other unique identifier we all posses, an email address. Just send me an email and I'll give you my contact details or send you instructions for meeting up. That is of course if you can make your email stand out from amongst all those Mydoom messages.