Secure, private, cloud-based messaging for iPhone and Android.
#messaging
Tropo
“Tropo is a powerful yet simple API that adds Voice, SMS, Twitter, and IM support to the programming languages you already know.”
Notifo
Pretty awesome, super-simple API-based service for sending notifications to distributed devices. Has an iPhone + Growl app.
PubSubHubbub
Google Code project page for PuSH.
messagepub
Interesting looking messaging platform (SMS, email, Twitter, GTalk, AIM, Phone). Fully API-accessible, but billed 1c per credit (up to 10c per message!)