The text messaging functionality in ActiveDEMAND uses local numbers for sending your automated texts. The actual sending of the text messages is done by the telecommunication networks (telcos).
The telcos watch local messaging to ensure that their numbers are not sued for mass text messaging. If they detect that the numbers are being used for mass texting, they will block the delivery of your text messages and revoke your ability to use text messaging for that number.
In short, do not try to send mass text messaging campaigns. You will more than likely have your sending number blocked by the telcos.
Using text messaging in a drip campaign for example, is useful. However, you will not be able to create generic campaigns with text messages as those campaigns typically involve a high volume of contacts.
For more information on the types of campaigns in ActiveDEMAND, please view this article.