I've left the unnecessary details out of the diagram - the important bit is that you can send email to people's phones. Once you've got that part down the rest is pretty straightforward - if you can do it on email, you can pretty much do it on phones, with the caveat that if you use very little text it will be much more popular. (Because who likes typing on their phone, really?) With this spirit in mind I mixed a simple mailing list and a publicly available email-to-SMS gateway to create some potent party madness to celebrate my birthday. The result was a series of SMS text messages sent out over the course of the evening to 65 people who'd previously given me their cell #'s. These messages let everyone follow the group from bar to bar, peeling off and reconverging as the night progressed. It also let me send out entertaining "challenges" as we went, such as:

"We are ninja!! Everybody stand on one leg. The last person standing gets three points."

The system was ridiculously easy to set up; a good friend of mine (who coincidentally runs my email service) helped me set up a Mailman listserv, which we called NinjaMonkey. I solicited phone numbers from my 200+ closest friends at NYU's ITP program, and appended "@teleflip.com" to the end of each number before group-subscribing them to the list. Teleflip.com is one of many publically available email-to-SMS gateway services; the idea is that you send email to an address consisting of the cellphone number you want to SMS plus the suffix "teleflip.com" (i.e., 1231231234@teleflip.com), and they automagically send it to the right cell phone carrier, who sends it on to your phone as an SMS. The result was that any email I sent to ninjamonkey@wireless.is got forwarded to everyone's cell phone on the list. This meant that I could send email from any machine (including, in this instance, my phone) and have it go to everyone else's phone, a phenomena known as many-to-many:

There were a few caveats and one final fubar. First, your phone has to support SMTP (standard email). I've got a lovely Nokia 6620 which lets me do just this, so I sent myself 15 or 20 "challenges" before the party and then forwarded them on to the NinjaMonkay listserv during the party as the mood caught me. This was a lot easier than typing in that much text on my phone's keyboard. I was also able to send out on-the-fly messages, such as the location of the next bar we were headed for.

One downside to all this was that because I had group-subscribed them people couldn't unsubscribe from the list themselves. As a result there were a bunch of people, some of whom were out of state, who were getting party messages until the wee hours.

Another problem was that the group of people I invited all tend towards the clever, and at least three individuals figured out how to hack the system. I had set up the listserv so only the admin could send messages out to prevent everyone from spamming each other as the revelry ramped up. It turns out, however, that if you spoof the outbound email address to make it look like I had sent the messages the list will automatically forward it along. This meant that those messages got approved, and sent out to the list, and I was sung Happy Birthday - a lot.

These problems aren't big problems, though, and are pretty easily solved - having people sign up on their own for the listserv would have enabled them to unsubscribe themselves if they couldn't make it to the party, and using an unusual email address to send from would have kept folks from guessing what I sent as (the listserv can also rewrite sent message address headers). But the one thing I hadn't planned on, and what finally killed the party at around 3am, was some pretty fundamental physics. The last challenge that I sent out to the list was:

"Make up a song about your favorite bar and present it to your charming Host (or Hostess). We go to winner's choice!"

The winner chose a bar underground, where there was no cell coverage. As a result nobody who wasn't already with us could find us, and the coordination (and the group) dissolved. Still, it was a good example of what you could do with a few simple components. Mix in a little fancy text munging along the way (say, with a mail server and some cgi's) and all of a sudden you've got a big, fluid group of people who can drop in and out of the group and communicate and query information on an as-needed basis; an instant social network. What more could a good little Ninja Monkey want?