Remind101 from remind101 on Vimeo.
Remind 101 even comes with pre-made handouts to give to students/parents instructing them how to use it's features.
Cel.ly - Cel.ly is a very similar, free, text messaging service that was featured on this Learn it in 5 video below:
Follow My Teacher - FMT is like a social classroom network with text messaging and email notifications built in.
Classroom social networks can easily facilitate communication between teachers, students, and parents. My 2 favorite are:
Two other popular group messaging services that are not used by teachers but provide similar services are: