Many cell phones can't do SMTP-AUTH.  The problem is avoided in any event by
using the smarthost (outgoing SMTP server) of your carrier, which in the case
of Cingular is either:
* photo.mycingular.com (adds a photo messaging footer)
* cwmx.com (preferred, no footer, an alias for wcmx.mycingular.net and
atlmx.mycingular.net)