“Tropo is a powerful yet simple API that adds Voice, SMS, Twitter, and IM support to the programming languages you already know.”
#sms
Notifo
Pretty awesome, super-simple API-based service for sending notifications to distributed devices. Has an iPhone + Growl app.
Email to SMS Gateways
Pretty exhaustive list of email gateways for phone providers around the world.
messagepub
Interesting looking messaging platform (SMS, email, Twitter, GTalk, AIM, Phone). Fully API-accessible, but billed 1c per credit (up to 10c per message!)
kwiry – text it before you forget it
kwiry – text it before you forget it
Pretty cool mobile-to-web service for reminders, triggering actions (like adding something to Netflix queue) etc via SMS.
SMS through E-Mail
Email address templates for routing emails to SMS messages on all the major US carriers.
twttr
simple moblogging/social networking from your phonr