Just for the sake of argument, let's say that to at least a dedicated technophile, things like cell numbers and email addresses could become enough a part of their personal identity that they could constitute a True Name.
OK. Even so, just knowing that number or address wouldn't be enough, in the same way that grabbing the name "Harry Blackstone Copperfield Dresden" from a phone book would be enough. Lots of people know Harry's name. But in the novels, it requires Harry to deliberately speak his name (or part of it) for someone to gain access to his True Name (or part of it). It's not the words themselves that constitute the Ture Name, it's that expression of the person's self wrapped up in his revelation of his identity that matters.
So I could easily see some people as tying themselves so strongly to an email name, forum handle, etc that it could become their True Name. But even so, a wizard would have to hear them deliberately speak that name in person for it to be used in magic. A recording, email list, business card, etc wouldn't cut it.