You can start a SMS and include multiple groups and friends, with a maximum of 30 people. For example, text jo cin volleyballers pledgegroup1 . Party tonight!
When starting a conversation with more than 8 people, you will be asked to select Reply-All (everyone receives replies) or Broadcast (initiator's messages go to everyone but replies only go to initator). NOTE: For Broadcast, all of the initiator's messages to the 3jam conversation, including replies, are sent to all members in the conversation.
Nothing else available today comes close (this includes voice calls, email, mobile email, IM, mobile IM, and push to talk). Start a 3jam and see for yourself!