Cingular is messed up and has a few email addresses. mobile.mycingular.com doesnt usually work. Most of the time cingularme.com works though. Also, former AT&T wireless customers should not be using mobile.att.net or a Cingular email, but mmode.com instead.
While its a little different than Teleflip, http://www.TxtDrop.com
lets you send FREE text messages from the web and uses these email addresses to send the messages.