I am a fan of IRC. For anything other than one-on-one chats, it seems to behave better than anything else I've tried, especially better than any of the "chat" functions I've used in various fora. A private IRC server is better than one of the public ones -- you're much less likely to receive unsavory invitations. (And anyone who *wants* those unsavory invitations is welcome to visit one of those servers if they wish; they don't need a #mobileread channel to intice them.
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I know someone who runs a private IRC server; he's a true geek and really into cool technology. (Know anyone else who has had multiple T1 circuits into his home?) I'm forwarding his contact information to the editorial team using the "Contact Us" form.