Sometimes you need to get the word out, but don't want to have to spend all day doing so. Sure, you can set up mailing lists and hit everybody at once, but how about going the next step, and having your contacts receive automatic updates?
TextMarks lets you create and manage text alert lists. Pick a unique keyword, and tell TextMarks what you want it to tell people about. Then when people text your keyword to 41411—maybe "Suzy50BDay"—they will get a message back about when and where the big party is. With the option to have people subscribe to your keyword, you can push updates out to them—whenever you tweak the content for their keyword, they'll get the latest sent to them.
If you really want to get into it, they've got an API that will let you do more than just send messages—you can ping a server or grab a bus schedule—but that requires some programming on your part.