Seriously… Why haven’t we seen this yet? This is the perfect application for the dashboard. Send text messages to your friends / family from the comfort of your computer without having to leave a tab open, or have yet another application running on your menu bar. You could have a growl plugin for it to notify you of messages. Maybe even a Firefox plug-in that click’s to call phone numbers.
To me this seems like one of a very few applications that would be really useful for a dashboard type setting. What do you think? What would you like to see?