You are charged per outgoing and incoming text message. This includes auto-responses, single text messages, system text messages, STOP or START text messages and group or entire list text messages.
Enhanced Text Messages (MMS)
Enhanced text messages are two (2) credits. You can send up to 300 characters with an image. If you send to 100 people, you will be charged for 200 text messages.
Standard Text Messages (SMS)
Standard text messages are one (1) credit. You can send up to 160 characters with no images. If you send to 100 people, you will be charged for 100 text messages.