Thanks to all....

I should have mentioned that the folks who I'd like to be able to group text are all on different carriers with different phones (and a couple of them don't yet have smartphones).

And that will certainly be the case when/if it grows to all the members of the organization.

I suppose I'm looking for something like a listserv for SMS (think Constant Contact or MailChimp) where I can add cell numbers on a website and send a mass text via that website or, if possible, via sending to an email address linked to the "listserv."

And re the Twitter suggestion, I have no idea how one would go about this with Twitter. Do all the recipients have to be on Twitter? Would they all have to set up their accounts to receive SMS notifications?