We are gearing up for an initial gathering in the Twin Cities based on this interest - http://groups.drupal.org/node/251383 - and I'd like to point people toward VOIP Drupal - http://groups.drupal.org/voip-drupal - implementations connecting small groups of people in two-way communication.
It would be great to point to an example of a small group that allows users to connect two-way in online groups with user-based notification options to receive (and send) e-mail, SMS, or a text to speech voice calls based on online group activity (or of course go to the website). Ideally, there would be a normal delivery channel and an urgent delivery channel option that allows for more broadcast levels of notice. Alternatively, there would be customizable keyword alert options SMS/Voice call could be selected.
Scenario: Announcing a neighborhood BBQ would only go out via voice call (instead of e-mail) to those who are in the system but don't have regular Internet access or those who requested it, while a note saying "XYZ neighbor is having a heart attack, all CPR trained neighbors please come to ABC address" would go via SMS and/or robo-call immediately to all folks in the online group. (We will leave tagging people's skills in emergencies until later.) The BBQ reminder one hour ahead of time could be a broadcast option too - "bring beer" is pretty urgent.
Also, in terms of OG Mailinglist, if there is an install that uses it - http://drupal.org/project/og_mailinglist - that would be nice to learn about. If not, any pointers on other two-way group e-mail communication options integrated with VOIP Drupal using other modules or what kinds of many-to-many group communication options that include e-mail that are native to the module that we can see live.
(Why all this e-mail stuff? E-Democracy's approach is to allow publishing through multiple channels and the idea is that firstname.lastname@example.org from X registered person would be routed to the right neighbors. Being able to simply say, just e-mail X, SMS Y or call Z and your message will automatically get to your group of nearest neighbors via the channel they prefer is the lowest common denominator vision I am suggesting. Also email@example.com would go via the urgent channel.)