Auto Responders are used in conjunction with drip Campaigns, as well as Web Forms. Message Type can be SMS text messages, Voice Broadcast calls, and/or Ringless VoiceMail drops.
When a Contact is added to a specific Group, they can receive a series of messages in a drip sequence. For example, they can receive an immediate welcome SMS message, followed by a Voice Broadcast call on Day 2, etc.
Once your Auto Responders are built, you can then add them to a Campaign.