Text messaging is a great way to communicate with parents. You can use these messaging services to send out urgent messages and reminders.
Class Messenger
You can send messages to parents and students - whole group or individual basis. You can send picture messages.
ClassDojo Messenger
Messages can be sent to individuals or an entire group. Parent do have to opt-in to receive messages.
ClassTag
You can email SMS/text messages to parents. This service does track whether or not they are opened and read by parents.
Remind
Students and parents can sign up to receive text messages on their mobile devices. You can attach files and create groups. Formerly know as Remind 101.
SeeSaw Messages
Messaging is a new feature added to this digital portfolio service.