A company named Odeo released a new service called Twttr, which is a sort of “group send” SMS application. Each person controls their own network of friends. When any of them send a text message to “40404,” all of his or her friends see the message via sms.
People are using it to send messages like “Going grocery shopping” and “at a party”. You can also add friends via text message, nudge friends, etc. It's really a social network around text messaging.
It's a cool service, but I don't like the fact that every user has a public page in which those messages appear and I can imagine that not everyone will want all their messages posted publicly. Also, if you are interested in this service I reccommend you enroll in an unlimited text messaging plan because this will service will cause substantial damage to your bank account with cell phone provider's $.10 sending/receiving plans.
I probably won't use this service much, if at all anymore, but check it out and you may like it.