This can be accomplished on twitter with a combinator of Twittermail.com and Twitpic.com, however I'm looking for a web-app that will allow for easier SMS access (ATT users have to use an SMS gateway code to send emails from their phones) and will allow for me to create a non-public feed.

Ideally, the solution would not require the SMS/emailers to sign up in any way (a la twittermail), and would operate without any moderation (I trust the audience).

Present.ly comes close, Yammer as well - perhaps I'm looking at services that too closely target dynamic user interaction.

Suggestions?