Here's a big list, some of which may be out of date:
http://www.livejournal.com/tools/tex...l?mode=details
It descirbes how each one works. The one I was looking for was Cingular, which is
[email protected] I usually send through the web interface which I have bookmarked (and each company usually has one of these), but sometimes the email is easier, sure.
Here's info on Teleflip:
http://www.teleflip.com/ I can't figure out from anything on the site why they have done this or how it supports itself. One article from a couple years ago (linked from the site) mentions it as a labor of love and may never have a commercial side. It only works in North America, by the way. That much is explained on the site.
EDIT: I thought the Cingular one was going to turn out to be wrong, but it did eventually work. There was a good 5-minute delay from send to receive. Teleflip came through immediately. Interesting.