The number alone is significant. And more mobile social networks (or services for phone-based socializing) are mentioned in the reader comments below this item in ReadWriteWeb.com. They're the services that want to be "the MySpace of the mobile Web," as Sarah Perez of ReadWriteWeb put it in another post. Twitter's not even on that list of 10 – is that because they're distinguishing between mobile (cellphone) blogging and mobile socializing (I think there's a fine line between the two, but maybe that's because I'm following the advice of author/professor Daniel Solove and trying to think less in terms of binaries such as online vs. offline, blogging vs. socializing, private vs. public and thinking in more granular ways)? Why is the growing number of phone-based social services significant? According to Perez, "InStat is predicting that by 2012, there will be nearly 30 million 'millennials' [Gen Y-ers or people born between the mid '80s and the mid-'90s] in the US using a mobile social network of some sort, and a ComputerWorld report confirms that, worldwide, that number will soar to 975 million by 2012." Any "millennials" in your family are quite likely to be among them.